Mountain rescue teams were searching for stranded competitors on Saturday after an elite marathon was called off because of heavy rain, flooding and high winds.
The athletes were competing in the Original Mountain Marathon (OMM), a two-day race across rough country in Britain's Lake District, about 300 miles north of London.
High winds and heavy rain affected much of northwest England on Saturday.
According to the marathon's website, the race was called off just after noon on Saturday, the first time in the race's history.
It's unknown how many people are stranded in the mountains as there is no mobile phone reception there.
Rescue teams would not be using Royal Air Force search-and-rescue helicopters because of the high winds, a member of the mountain rescue team said.
Rivers in the area burst their banks and fast flowing water filled most of the valley by mid-afternoon closing roads.
In a statement, Cumbria Police said about 840 people had taken shelter in four different locations in the area, including a school, farm, and outdoor center.
"The competitors are mainly seasoned mountaineers, and are expected to be carrying suitable equipment to cope with adverse weather," the release said.
The OMM website says the race was founded in 1968.
Teams are "totally self-supporting," and competitors do not carry global
positioning systems or mobile telephones.
Competitors race in pairs and carry their tents, clothing and enough food for 36 hours.
"The ethos of the event is to be totally self-reliant, in the wilds, carrying all equipment, no outside support," the website states.
One man who manages a mine in the area, said he had sheltered about 300 athletes from horrendous weather and described a scene of chaos on the mountain.
The sleepmonsters.co.uk website, which filed reports on the race, said conditions had deteriorated throughout the afternoon.
None of the race organizers were immediately available for comment.
According to local hospitals and rescue services, more than a dozen people were treated for minor injuries and mild hypothermia.