Forecasters in Colorado are warning residents near Denver to brace for torrential overnight rains, as raging flood waters roar through the region and cloud cover hampers helicopter rescue efforts.
Days of heavy rains and flooding have turned the state's Rocky Mountain foothills into high risk zones, with dozens of washed out roads and bridges turning entire communities into disaster areas short on supplies and services. At least four people were known dead by late Sunday, with two others officially missing and presumed dead.
Authorities say about 500 people were unaccounted for Sunday, while cautioning that some may be unable to communicate with loved ones while stranded and awaiting rescue.
Rocky Mountain rescue management officials say as many as 1,000 people were awaiting rescue north of Denver, in an area that includes the hard-hit mountain community of Estes Park. But all airlifts were grounded Sunday because of new rains and poor visibility.
Local news outlets say 50 bridges linking rural communities have been destroyed or damaged, and warn of a growing threat from mudslides and rockslides as roads crumble. Boulder County Sheriff Joe Pelle, speaking to reporters Saturday, said authorities were only beginning to understand the scope of the crisis.
President Barack Obama has declared Colorado a major disaster zone and ordered federal help to boost state and local recovery efforts.
Helicopters have plucked hundreds of people from inundated homes. One helicopter carrying Colorado Governor John Hickenlooper on a tour of the region made two stops to pick up residents waving to be rescued on Saturday.