A Chinese shepherd has been hailed as a hero for saving six runners in an ultramarathon race in which 21 died.

Zhu Keming said he was grazing his sheep on Saturday in the northern province of Gansu when rain began to fall and temperatures plummeted.

Nearby, the sudden weather change had caught out runners in a 100km (60-mile) cross-country race.

Mr Zhu took refuge in a cave where he stored emergency food and clothes, but while inside he saw a stricken runner.

The shepherd told Chinese state media that he escorted the runner into the cave, massaged his hands and feet, and lit a fire to dry his clothes.

Four more distressed runners made it into the cave and told the shepherd others were marooned outside, some unconscious, AFP news agency reported.

Braving hail and freezing temperatures, Mr Zhu went out to search and saved another stricken runner.

"I want to say how grateful I am to the man who saved me," the runner, Zhang Xiaotao, wrote on Chinese social media site Weibo. "Without him, I would have been left out there," he said.

Mr Zhu ultimately rescued three men and three women, according to the reports. He told state media he was "just an ordinary person who did a very ordinary thing".

"There were still some people that could not be saved," he said. "There were two men who were lifeless and I couldn't do anything for them. I'm sorry."

The controversial race has become a source of outrage in China after organisers apparently ignored warnings of extreme weather.

The race was halted and a massive rescue operation launched after reports that some of the 172 runners had gone missing.

Many of the stranded runners reportedly suffered from hypothermia, and had lost their way on the route as heavy rain and hail affected visibility.

Among the 21 competitors who died was Liang Jing, one of China's most accomplished ultramarathoners. Mr Liang was pictured beginning the race in just shorts, a thin jacket and a baseball cap.

The 31-year-old had won numerous long-distance races in China, including the Ultra Gobi in 2018 - a 400km race through the Gobi desert.

Another victim, Huang Guanjun, 34, was hearing-impaired and unable to speak, reports said. He was known for winning the men's hearing-impaired marathon at China's 2019 National Paralympic Games.

Surviving participants of the abandoned ultramarathon said the forecast had indicated there would be some wind and rain, but nothing as extreme as what they experienced.

The deaths have sparked public outrage on Chinese social media, with anger mainly directed at the local government in the city of Baiyin and unhappiness over the lack of contingency planning.

In a news conference on Sunday, Baiyin's Mayor Zhang Xuchen said: "As the organiser of the event, we are full of guilt and remorse. We express deep condolences and sympathy to the families of the victims and the injured.