A new wave of rain is threatening to hamper airlifts from flooded areas still out of reach in the US state of Colorado.
The widespread flooding has killed at least seven people, officials said on Sunday, as the search for people stranded from the Rocky Mountain foothills to the plains of northeastern Colorado grew more difficult.
About 1,500 homes have been destroyed and another 17,500 damaged, according to an initial estimate released by the Colorado Office of Emergency Management on its website.
In addition, 11,700 people have left their homes, and a total of 1,253 people have not been heard from, state emergency officials said.
Four people in Boulder County and one in El Paso are dead, and two women missing in Larimier County are missing and presumed dead.
President Barack Obama signed a disaster declaration on Saturday and ordered federal aid for the state.
Despite 1,750 people having already been rescued from communities and homes swamped by overflowing rivers and streams, numerous pockets of remain cut off from help, officials said.
Twenty military helicopters planned to expand the search from Boulder County east to Fort Morgan. But they were grounded as more rainstorms began on Sunday.
Al Jazeera's Jim Hooley, reporting from Boulder in Colorado, said on Sunday morning that heavy rain had already moved in.
"The rain is going to keep the rescue helicopters on the ground," he said.
The additional rain, falling on ground that has been saturated by water since Wednesday, created the risk of more flash-flooding and mudslides, according to the National Weather Service.
Further thunderstorms, lightning and torrential rain had been predicted for Sunday night in already flooded areas.
Meanwhile, authorities fear a rising death toll from the weather.
An 80-year-old woman in Larimer County's Cedar Cove was missing and has been presumed dead after her home was washed away by the flooding Big Thompson River, officials said on Sunday.
The woman was injured and unable to leave her home on Friday night, John Schulz, sheriff's spokesman, said.
"When local people came to help get her out of the home, it was gone," he said.
That is the same area where a 60-year-old woman is presumed dead after the river destroyed her home the same night.
The number of confirmed flood fatalities stood at four but was expected to rise.
Hundreds of people remained unaccounted for though most are likely just stranded, officials said.
The White House said in a statement on Saturday night that Obama's disaster declaration makes federal funding available to affected individuals in Boulder County.
The government said that other counties could be added later.
Obama called John Hickenlooper, Colorado's governor, for an update on the flooding and reinforced his commitment of federal aid for the flooding.
In Morgan County, Sheriff James Crone told KMGH-TV a bridge collapsed and the raging South Platte River divided the area.
|Al Jazeera's Ash-Har Quraishi reports from Colorado
The river was expected to flood until at least Tuesday, and Crone worried the new rain could send another surge of water down the river, Crone said.
"We lost every bridge crossing east to west and we are cut in half," he said.
The last two days have seen dramatic rescues of trapped residents as helicopters hoisted them and their pets above the floodwaters. Some have refused to go, choosing instead to stay with their homes and property.
Sheriff Joe Pelle of Boulder County said those people would not be forced to leave, but they have been warned that rescuers will not return for those who choose to stay.
Rescue crews in Larimer County planned a ground push Sunday to reach residents in Rist Canyon west of Fort Collins, Schulz said.
An unknown number of people there have been receiving food and water drops.
"We're sending crews up there as far as we can," Schulz said. "This is a very mountainous area."
PHOTO GALLERY: IMAGES FROM BOULDER COUNTY
Source: Al Jazeera and agencies