State officials in Australia have apologised for their failures over the handling of a huge Covid-19 outbreak on the Ruby Princess cruise ship.

Last week, an inquiry found New South Wales health authorities made "serious mistakes" in allowing about 2,650 passengers to disembark when the ship docked in Sydney in March.

Those people were not tested for the virus, despite suspected cases aboard.

The ship was ultimately linked to at least 900 infections and 28 deaths.

Prior to Australia's second wave of the virus - which emerged in Melbourne in June - the cruise ship had been the source of Australia's biggest coronavirus cluster.

NSW Premier Gladys Berejiklian said she was particularly sorry to the 62 people who had caught the virus from passengers who disembarked.

"I can't imagine what it would be like having a loved one - or being someone yourself who continues to suffer and experience trauma as a result - and I want to apologise unreservedly," she said.

What mistakes were made?

After completing an 11-day return cruise to New Zealand, passengers were allowed to leave the ship at Sydney Harbour and catch public transport, and domestic and overseas flights home.

An inquiry report released last Friday found NSW Health had mischaracterised the ship as low-risk, and should have tested sick patients immediately.

It was "inexcusable" that officials had failed to immediately obtain results from coronavirus swab tests taken on 19 March - the day the vessel docked.

However the inquiry found no systemic failures and said the mistakes had already been recognised by the state government.

Following the Ruby Princess debacle, at least a dozen other cruise ships were banned from docking at Australian ports due to their virus risk.

Most of the Australian passengers on the Ruby Princess self-isolated at home, in line with government instructions for returning travellers.

Excluding a cluster in the island state of Tasmania which spread through a hospital system, 62 people in Australia became infected through secondary transmissions.

Ms Berejiklian singled out those cases in her apology, saying: "Unfortunately in particular for those 62 individuals, the lessons weren't learnt soon enough."

At least a third of passengers - or around 950 people - were from overseas.

The inquiry said it was not able to fully assess how many people had caught the virus because many were unable to get tested.