The stock market slid 2.6 percent as investors fretted about what the latest troubling news meant for the economic recovery. That could lead some states to slow the reopening of businesses, further hobbling the economy and delaying its recovery.

As of Wednesday, 2.3 million Americans have been infected with the coronavirus, and 121,925 have died.

On Wednesday it was as if the country had found itself back in March — at the start of the pandemic, in the early days of the lockdown, when masks were in short supply and when the death toll was skyrocketing.

Gov. Gavin Newsom of California said that the state had recorded more than 7,000 new cases over the previous day.

In Washington State, where case numbers have again been trending upward, the governor said residents would have to start wearing masks in public.

“This is about saving lives,” said the state’s governor, Jay Inslee, a Democrat. “It’s about reopening our businesses. And it’s about showing respect and care for one another.”

In Florida on Wednesday, Gov. Ron DeSantis gave no indication that the state would roll back its economic opening, but he urged residents to avoid closed spaces with poor ventilation, crowds and close contact with others.

Mr. DeSantis, a Republican, continued to attribute the rising infections, especially in cities, to younger people who have started to socialize in bars and homes, in spite of rules in many municipalities prohibiting group gatherings. He pressed older people to keep staying home as much as possible, and pleaded with young people to be responsible.

“You need to do your part and make sure that you’re not spreading it to people who are going to be more at risk for this,” he said.

Arizona on Tuesday reported its highest number of virus hospitalizations, as did North Carolina, prompting its governor, Roy Cooper, to announce on Wednesday that the state would pause reopening for three weeks and require face masks. In Texas, more than 4,300 people with the virus are hospitalized, more than double the number at the beginning of June.

But in Missouri, where new case reports have reached their highest levels in recent days, coronavirus hospitalizations have declined slightly over the last month.

“We are NOT overwhelmed,” Gov. Mike Parson, a Republican, said on Twitter, linking the uptick to more testing. “We are NOT currently experiencing a second wave. We have NO intentions of closing Missouri back down at this point in time.”

The World Health Organization warned on Wednesday that if governments and communities in the Americas are not able to stop the spread of the virus through surveillance, isolation of cases and quarantine of contacts, there may be a need to impose — or reimpose — general lockdowns.

“It is very difficult to take the sting out of this pandemic unless we are able to successfully isolate cases and quarantine contacts,” said Dr. Michael Ryan, the executive director of the W.H.O. health emergencies program. “In the absence of a capacity to do that, then the specter of further lockdowns cannot be excluded.”

He said that the growing number of coronavirus cases in the Americas has not peaked and that the region is likely to see sustained numbers of cases and deaths in the coming weeks.

With cases surging in the Houston area, the city’s intensive-care units are now filled to 97 percent of capacity, Mayor Sylvester Turner told the City Council on Wednesday, with Covid-19 patients accounting for more than one-quarter of all patients in intensive care.

The city, known for its large concentration of medical schools and research hospitals, could run out of I.C.U. beds within two weeks if nothing is done to slow the upward trajectory of the virus, said Dr. Peter Jay Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine. He called on the state to reimpose more aggressive social distancing restrictions.

Dr. Hotez said that hospitalizations were rising along with the case counts, so the data is not just the result of increased testing. “That means we have to act this week,” Dr. Hotez said.

On Wednesday, Gov. Greg Abbott said in a television interview that more than 5,000 people had tested positive in the past day and that more than 4,000 were hospitalized. There is a “massive outbreak of Covid-19 across the state of Texas today,” he said.

Apple said it closed seven of its stores in the Houston area because of rising coronavirus cases in the region. The move on Wednesday followed its closing of 11 stores in Arizona, Florida, South Carolina and North Carolina because of the virus. Apple had closed nearly all of its roughly 500 stores worldwide months ago, but had opened most in the United States in recent weeks after cases declined. Just over 200 of Apple’s 271 American stores are now open, with some still closed because of damage from protests, an Apple spokesman said.

In other news around the United States:

• In Florida, which had a record number of new coronavirus cases on Wednesday, Gov. Ron DeSantis urged people to avoid closed spaces with poor ventilation, crowds and close contact with others. Total virus cases in Florida exceeded 100,000 on Monday, with more than 3,100 deaths. About one-quarter of the cases have been in Miami-Dade County, where the per capita rate is twice the number statewide. Still, Trump National Doral, which is in the county and is the most important source of revenue for the president’s strained family business, reopened last weekend.

• Gov. Roy Cooper of North Carolina, which reached a record 915 virus hospitalizations on Tuesday, announced on Wednesday that the state would pause its reopening for three weeks and require face masks in public. The state has more than 56,000 cases and nearly 1,300 deaths. Mr. Cooper said that hospitals had not reached capacity, but could quickly become overwhelmed. Also, a judge in the state ruled against the reopening of Ace Speedway, which state health officials had ordered to shut down, saying the racetrack had defied restrictions on the size of public gatherings.

• State officials in Virginia are proposing workplace virus safety rules that, unlike those in some other states, would be mandatory and backed by enforcement. Labor activists and state officials said Virginia was acting because the federal Occupational Safety and Health Administration had not issued enforceable standards or acted on thousands of complaints. The Virginia rules would impose physical distancing and sanitation requirements, and among other measures, companies would have to notify workers of possible exposure. Violators could be fined or shut down.

• Joseph R. Biden Jr. has taken a commanding lead over President Trump in the 2020 presidential race, building a wide advantage among women and nonwhite voters, according to a new national poll of registered voters by The New York Times and Siena College. Mr. Biden has made deep inroads into some traditionally Republican-leaning groups that have shifted away from Mr. Trump after his ineffective response to the coronavirus pandemic. He currently leads Mr. Trump by 14 percentage points, garnering 50 percent of the vote. Nearly three-fifths of voters disapprove of Mr. Trump’s handling of the pandemic.

• A judge in Texas who signed an order requiring everyone in the San Antonio area to wear masks was assaulted at a Lowe’s home improvement store on Wednesday after he confronted another customer who was not wearing a mask, the authorities said. When Judge Nelson Wolff tried to hand a card to the man, the other customer slapped away his hand, surveillance video released by the Bexar County Sheriff’s Office showed. It was not clear what the card said. The man, who also berated the judge, could face a felony charge of assault of a public servant, the sheriff, Javier Salazar, said during a news conference at the store.

• As California recorded its highest number of infections, Disneyland indefinitely postponed its plans to reopen in Anaheim on July 17. The Walt Disney Co. said that it was awaiting the state’s guidelines for reopening theme parks, which were not expected to be issued until after July 4. Thousands of workers at Disneyland and at Walt Disney World in Florida, which is scheduled to begin a phased reopening on July 11, have signed petitions calling on Disney executives to pause plans.

  Gov. Andrew M. Cuomo of New York announced on Wednesday that the state will begin requiring out-of-state travelers coming from hard-hit states to quarantine for two weeks upon arrival, a move that punctuated a stark shift in the course of the nation’s outbreak.

  The restrictions will be based on specific health metrics related to the virus, he said at a news conference. The quarantine would apply to travelers arriving from a state, as well as New Yorkers returning from a state, where there was either a positive test rate higher than 10 per 100,000 residents, or a state with a 10 percent or higher rate over a seven-day rolling average.

  “A lot of people come into this region and they could literally bring the infection with them,” he said. “It wouldn’t be malicious or malevolent, but it would still be real.”

  Eight states would be included, Mr. Cuomo said, when the restrictions took effect at midnight: Alabama, Arizona, Arkansas, Florida, North Carolina, South Carolina, Texas and Utah. Washington State had originally been included, but was dropped from the list after a further review of the data.

  Travelers returning to New Jersey and Connecticut from those states would also be told to quarantine; their governors appeared with Mr. Cuomo to announce a tristate “joint travel advisory.” Mr. Cuomo said that enforcement would be up to each of the three states. Officials from New Jersey and Connecticut said there was no enforcement mechanism at the moment in their states.

  In New York, those violating the quarantine order could be “subject to a judicial order and mandatory quarantine,” he said, and fines of up to $10,000. Mr. Cuomo also said that officials would not be stopping people at state borders to forbid them to enter, but that travelers were being asked to comply once they arrived.

  A spokesman for Mr. Cuomo said that if a New Yorker believes that a recent arrival — or a returning neighbor — has not been abiding by the quarantine, then that person should start by reporting the possible violation to the local health department. Elsewhere in the U.S. where there are similar quarantines for travelers, there has not been widespread enforcement.

  The goal, the governor said, was to maintain the hard-fought gains made in the region at great economic and human cost. For months, the state — New York City particularly — had been a global center of the pandemic. Hospitals filled to near capacity. Hundreds died each day, reaching a peak in mid-April. But on Wednesday, Mr. Cuomo said there were only an additional 17 deaths statewide.

  New York’s quarantine will not apply to Yankees and Mets players returning to the area to complete spring training, which can begin on July 1, Mr. Cuomo said, adding that the state had been working on separate “health protocols” with them since last week.

  Elsewhere in New York:

  • With the pandemic siphoning as much as $9 billion in tax revenue from New York City, Mayor Bill de Blasio and other top officials said Wednesday that the city might have to lay off or furlough 22,000 municipal workers this fall and make sweeping cuts in infrastructure spending.

  • The New York City Marathon has been canceled this year. City officials and organizers decided holding the race, the world’s largest marathon, would be too risky.

  • The mayor said that the city will close 23 more miles of streets to car traffic to provide more outdoor space while social distancing rules remain in place. The city’s beaches will also be open for swimming and recreation on July 1 but with required social distancing.

  • Five upstate regions are set to enter Phase 4, the final phase of the state’s reopening plan, on Friday, Mr. Cuomo said. Indoor gatherings of up to 50 people will be allowed, and some arts and entertainment venues can open. Malls, movie theaters and gyms must remain closed.

  • New Jersey officials said on Wednesday that bowling alleys, museums, arcades, aquariums, batting cages, shooting ranges and libraries may reopen at 25 percent capacity on July 2. Gyms stay closed, though individual appointments with trainers can be scheduled, said the governor, who reported 48 more deaths on Wednesday.

    The International Monetary Fund warned on Wednesday that the global economy faces an even deeper downturn than it previously projected as the coronavirus pandemic continues to sow uncertainty and businesses around the world struggle to shake off the virus.

    The forecast underscores the scale of the task that policymakers are facing as they try to dig out from what the I.M.F. has described as the most severe economic contraction since the Great Depression. Even as countries begin reopening their economies, it is increasingly evident that the recovery will be uneven and protracted, particularly until the virus dissipates or a vaccine becomes available.In an update to its World Economic Outlook, the I.M.F. said it expected the global economy to shrink 4.9 percent this year — a sharper contraction than the 3 percent it predicted in April. The fund noted that, even as businesses began to reopen, voluntary social distancing and enhanced workplace safety standards were weighing on economic activity. Moreover, the “scarring” of the labor force from mass job cuts and business closures means that the world economy will recover much more slowly, with the I.M.F. projecting 5.4 percent global growth in 2021, far below its pre-pandemic projections.

    
    The I.M.F. now projects that the U.S. economy will shrink 8 percent this year before expanding 4.5 percent next year. Economies in the eurozone are projected to shrink 10.2 percent this year and expand 6 percent next year. The economy of China, where the virus originated and which imposed draconian containment measures, is expected to expand 1 percent this year and 8.2 percent in 2021.

    
    In the markets on Wednesday, the S&P 500 fell more than 2 percent by midafternoon, erasing gains from earlier in the week, as investors confronted new signs of the pandemic’s persistence. Shares of retailers, airlines and cruise companies — which are proxies for sentiment about the prospects of a recovery — are faring poorly. Nervousness about the economic outlook was evident in oil prices, and shares of energy companies also declined.