The rescue headquarters quoted by the official Xinhua News Agency said participants suffered from physical discomfort and the sudden drop in temperature.
Some went missing in the extreme weather around 1 pm Saturday, when the 100-kilometre race in the Yellow River Stone Forest tourist site in Baiyin city in Gansu province was halted.
By early on Sunday, 20 people had been found dead and one was missing, state broadcaster CCTV reported.
More than 700 rescuers were taking part in the operation, made difficult by low night-time temperatures and the area’s complex terrain and topography.
A total of 172 people joined the race and 151 are confirmed to be safe.
Some were treated for minor injuries and were stable, Xinhua said.
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