BEIJING — Twenty-one people running a mountain ultramarathon have died in northwestern China after hail, freezing rain and gale-force winds hit the high-altitude race, state media reported Sunday.

After an all-night rescue operation in freezing temperatures involving more than 700 personnel, rescuers were able to confirm that 151 people were safe, out of a total of 172 participants. Twenty-one had died, according to the official Xinhua News Agency, which said the runners suffered from physical discomfort and the sudden drop in temperature.

The runners were racing on an extremely narrow mountain path at an altitude reaching 6,500-9,800 feet. The 60-mile race was held Saturday in the Yellow River Stone Forest tourist site in Baiyin city in Gansu province. The participants were not rookies. One of the deceased was a well-known runner Liang Jing, who had won a 62-mile race in Ningbo, reported the Paper, a state-backed newspaper based in Shanghai.

The race also followed a relatively established course, having been held four times, according to an account posted online by a participant in the race who quit and managed to make his way to safety. But the weather caught them off guard, and on the morning of the race Saturday, he already sensed things were not normal. The runners were not dressed for winter-like conditions, many wearing short-sleeved tops.