“Extreme weather hit the area during the race” being held in the Yellow River Stone Forest near Baiyin City in northwestern Gansu province, Xinhua said, adding that more than 700 rescuers were deployed to find the missing runners.

“According to the rescue headquarters, at about 1pm Saturday, hail, freezing rain and gales hit the area of the race’s high-altitude stage between 20km to 31km,” the agency reported.

“Participants suffered from physical discomfort and loss of temperature due to the sudden drop in air temperature.

“Some of the participants went missing and the race was halted,” it said.

Temperatures in the mountainous terrain dropped further overnight, Xinhua said, making search and rescue “more difficult”.

“As of 3am Sunday, 151 participants have been confirmed to be safe, of which five with minor injuries are being treated in the hospital and in stable condition,” it said.

The People’s Daily newspaper gave a slightly different toll of 15 dead with six still missing.

Gansu, one of China’s poorest regions, borders Mongolia to the north and Xinjiang to the west.

Deadly floods and landslides have hit the province in the past, with mudslides reportedly killing well over 1,000 people in one town in 2010.

It is also prone to earthquakes.

Yellow River Stone Forest is famous for its rugged mountain scenery marked by stone stalagmites and pillars, and is used as a location in many Chinese television shows and movies, according to the China Daily.

Its rock formations are believed to be four billion years old, the Daily said.

Xinhua said a total of 172 people were taking part in the race.