Rescuers have recovered the bodies of 21 runners after disaster struck an ultramarathon in China ©Getty Images

Twenty-one people have been confirmed dead after extreme weather hit an ultramarathon race in China.

The were 172 runners taking part in the cross country race in Gansu, and two of China's best long-distance runners - Liang Jing and Huang Guanjun - are reported to be among those killed.

According to rescuers, as reported by state-run media outlet CGTN, hail, freezing rain and strong gales struck the race's high-altitude section, between kilometres 20 and 31 of the 100km route.

The race was held yesterday morning, starting at the Yellow River Stone Forest tourist site near Baiyin.

Extreme weather hit the race around 1pm local time, with participants reportedly suffering physical discomfort and loss of warmth due to the sudden drop in air temperature.

The race was halted when some of the participants went missing, leading to an emergency response which saw more than 700 rescuers search for the unaccounted.

"At around noon, the high-altitude section of the race between 20-31km was suddenly affected by disastrous weather," said Baiyin City Mayor Zhang Xuchen.

"In a short period of time, hailstones and ice rain suddenly fell in the local area, and there were strong winds.

"The temperature sharply dropped.

"This incident is a public safety incident caused by sudden changes in weather in a local area."

Organisers have faced criticism on Chinese social media for allowing the race to go ahead, with one commentator questioning whether the weather forecast was read and a risk assessment carried out.

Gansu, one of China's poorest provinces, borders Mongolia to the north and the province of Xinjiang to the west.