At least 21 participants in a mountain marathon in northwest China were killed in extreme weather.

Eight other participants in the ultramarathon in the tourist attraction of the stone forest on the Yellow River in Baiyin were taken to hospitals for treatment, Chinese state media reported on Sunday.

On Saturday, the marathon in Gansu province led over 100 kilometers over mountains through impassable terrain.

However, the 172 participants experienced a severe weather change with freezing rain, hail and squalls about 20 to 30 kilometers after the start.

The temperatures dropped drastically within a very short time. The storm simply blew away warming blankets made of emergency equipment that the runners, some of whom only dressed in shorts and T-shirts, had carried, reported the state media. Many runners got lost on the steep terrain, collapsed hypothermic and exhausted. Participants desperately called for help on cell phones. "Come to the mountains to save the people," one wrote in a text message. "Too many are cold and lost."

"We are in a ravine," wrote another. "A runner suffers from hypothermia and can no longer move." It was also reported: "Some are unconscious". The calls for help also said: “It's tragic” and “Come as soon as possible!” Or “The wind is too strong”. The local authorities canceled the marathon and organized a rescue operation with 1200 helpers, which lasted overnight until Sunday, according to state media.

The search was very difficult in the impassable terrain, up to 2000 meters high. Only the first 24 kilometers of the route were passable by car. The temperatures also continued to drop overnight. State media said drones with heat sensors were used to track down missing people. Runners returning from the mountains reported that near the second checkpoint, freezing rain suddenly fell and strong winds came up. Some cried, shaken, and reported seeing exhausted runners lying on the ground.

The provincial government set up a special commission to investigate the incidents.

"As the organizers of the event, we feel deeply guilty and blame ourselves," said Zhang Xuchen, the mayor of Baiyin, at a press conference.

"We extend our deepest condolences to the victims and their families." The search was concluded on Sunday morning.

All the missing were found.

151 participants in the marathon are safe.

The 100-kilometer mountain marathon in the picturesque tourist region has been held annually for four years together with two shorter cross-country runs of up to 21 kilometers.

The Hong Kong newspaper "South China Morning Post" reported that nearly 10,000 participants had registered for the three different runs.