More heavy rain is expected in the American state of Colorado, where the worst floods in decades have killed at least four people and left 172 unaccounted for.
Search and rescue teams have used boats and helicopters to pull stranded residents to safety in areas where flash floods toppled buildings, washed out roads and inundated farmland.
The body of a woman was found after she was swept away from her submerged vehicle on Thursday, authorities say, bringing the death toll to at least four. A man and his dog who were swept into a pipe were both rescued alive.
Reuters reports the flooding was triggered by unusually heavy late-summer storms that soaked Colorado's biggest urban centres, from Fort Collins near the Wyoming border south through Boulder, Denver and Colorado Springs.
Boulder and a string of other towns along the Front Range of the Rocky Mountains north of Denver were especially hard hit.
State governor John Hickenlooper says he's never experienced such severe flooding and weather forecasters say more rain is coming as records continue to be broken.
Days of heavy rain have caused severe damage to property and forced the rescue of more than 2500 people, Boulder County officials say. Water levels in the Boulder Canyon rose rapidly because of debris and mud blocking its mouth.
The raging torrent - dubbed a "100-year flood" by officials - has prevented rescue crews from reaching communities stranded downstream.
The BBC reports more than 38 centimetres of rain - nearly half the region's annual average - has fallen in a single week, according to the National Weather Service.
President Barack Obama has signed an emergency order approving federal disaster aid for Boulder County.
Towns such as Jamestown, Lyons and Longmont are said to have been reduced to islands by the swirling floodwaters, reports the BBC. Officials set up road blocks to prevent some residents fleeing in their vehicles over submerged or debris-strewn roads.
Part of US Highway 36 is closed after it was washed out by floodwater and Colorado officials shut Interstate 25 north of Denver all the way to the Wyoming border.
The BBC reports the prolonged rain is blamed on a low-pressure system over Nevada, which is drawing moist air out of Mexico into the foothills of the Rockies.