Twenty-one runners taking part in the 100-kilometer cross-country mountain marathon race on Saturday in Baiyin City, northwest China's Gansu Province have been confirmed dead, according to rescuers.

The race took place in the Yellow River Stone Forest tourist site in Jingtai County and was hit by extreme weather including hail, freezing rain and gale-force winds. The deceased suffered from hypothermia due to the sudden drop in air temperature, local rescue headquarters said in a media briefing on Sunday morning.

Victims included Liang Jing and Huang Guanjun, two of the top domestic marathon runners of the country. Liang won the championship of the Ultra Gobi non-stop race in 2018; Huang won gold in the marathon of the hearing-impaired section of China's National Paralympic Games in 2019.

The stone forest race was first launched in 2018 and was named a bronze medal event by the Chinese Athletic Association. It contained three competitions that are five, 21 and 100 kilometers respectively.

Cross-country marathon is a high-risk sport that has significant requirements for participants. For example, one must provide a finishing certificate from similar-level race that was attained within a year in order to qualify for the race. The minimum age for the 21km group is 18-years-old and the maximum age for the 100km group is 60-years-old.

The race is still a challenge for qualified runners because it takes place at an altitude of around 2,000 meters. Most of the site is depopulated. Moreover, one must reach the goal within 20 hours to finish it.

There are nine checkpoints set for the 100km race and the accident happened between Checkpoint No. 2 (24 kilometers) and Checkpoint No. 3 (32.5 kilometers). It's one of the hardest parts of the course as participants have to go through a long slope made of sand and rocks.

The extreme weather made it even more difficult and dangerous. Many quit the race but some were trapped in steep locations. Strong winds tore their thermal blankets apart, accelerating the loss of temperature.

The weather forecast on Friday did not warn about the extreme weather, reported The Paper after contacting one of the participants. Wind began to grow strong soon after the race had begun and it rained more and more heavily, further lowering the visibility, when the anonymous runner reached Checkpoint No. 2.

The participant said he could not feel his fingers when he reached the middle between Checkpoint No. 2 and Checkpoint No. 3. "I put my fingers in my mouth for quite a while but I still felt nothing. My tongue was freezing too," said the participant. "I decided to quit immediately but it's hard to get down from where I was, it's too steep."

The runner told The Paper he noticed that the compulsory kit list did not have enough thermal equipment and that may be one of the reasons many participants froze.

The Paper learnt that May 22 is usually summer in Baiyin City. During the previous editions of the race, the organizers did not make it mandatory for runners to take outdoor jackets and other gear along with them. They were only recommended in the playbook. Before Saturday's race, the organizers were more worried about heatstroke than cold weather.

Zhang Xuchen, mayor of Baiyin City, apologized to the families of the victims and injured athletes on behalf of the host.

"This is a public safety incident caused by sudden change of regional weather. As the event organizer, we are in deep regret and remorse. We apologize to the families of the victims and injured [athletes] and our condolences go to you. The provincial government has also set up an investigation task force to follow up the investigation," said Zhang on Sunday.