Rescuers have rushed by land and by air to evacuate people in the US state of Colorado stranded by worst mountain flooding in decades, with hundreds of people unaccounted for, authorities say.
Relentless rains pounded flood-ravaged areas for a fifth day on Saturday, triggering more evacuations and warnings as rescuers tried to reach thousands of people displaced or stranded by the deluge that has been blamed for at least four deaths.
Many, many communities in our western mountains are completely isolated. There is no road access, no telephone information, no power, no water, no sewer
Flooding from days of unprecedented rainfall in the semi-arid region has destroyed homes and closed or washed out bridges and roads from mountain canyons from metropolitan Denver to the eastern plains.
A surge from swollen rivers and creeks has flooded downstream farming counties in northeastern Colorado, prompting
the evacuation on Saturday of several towns along the South Platte River.
"This is a 500-to-1,000-year flood," Sean Conway, a commissioner of rural Weld County, said at a news conference.
The Denver Post newspaper, citing the Boulder County Office of Emergency Management, reported that the number of people who were unaccounted for had risen to 350 by Saturday afternoon, up from 230 earlier in the day.
Patrick Von Keyserling, an emergency official in Boulder, an area heavily affected by flooding, said the number will fluctuate as families start locating people and as rescue teams pick up people with helicopters that have been stranded
"We will continue throughout the day as long as the weather is permitting" he told Al Jazeera.
"Certainly the intent is to find all unaccountable people. Some may be at rescue centres or staying with relatives," Von Keyserling said.
The military put more troops on the ground and helicopters in the air to aid in the search-and-rescue effort, as rescue team on boats tried to find residents still missing.
Power cut off
More than two months' of rain fell in less than two weeks, cutting off communities from power and clean water. The flood zone has grown to cover an area of about 11,655 square kilometers, nearly the size of the US state of Connecticut.
Four people are confirmed dead from the flooding, and a fifth victim, a 60-year-old woman, is missing and feared dead after witnesses saw her mountain home swept away by floodwaters, authorities in Larimer County said.
National Guard helicopters and truck convoys broke through to paralysed canyon communities where thousands of stranded residents were eager to escape the Rocky Mountain foothills.
Some areas have seen more than 15 inches of rain in a span of three days, which is above average rainfall totals for an entire year, the National Weather Service said.
| Al Jazeera's Ash-Har Quraishi reports from Colorado
Motorists were trapped in their cars with emergency crews scrambling to reach them.
"Many, many communities in our western mountains are completely isolated. There is no road access, no telephone information, no power, no water, no sewer," said Sheriff Joe Pelle of Boulder County.
In Lyons County, many residents have had no access to clean water or power for two days. The area lies near the meeting point of two rivers, and days of flash floods have made it resemble an inland sea.
Further downstream in Morgan County, the farming communities of Weldona, Goodrich, Muir Springs and Orchard were under evacuation orders.
National Guard troops have joined local emergency crews stretched thin by the scope of the disaster to team up on search and rescue missions.
Rescue crews got a break when the rains let up on Friday, but by Saturday afternoon the rains returned, prompting the National Weather Service to issue flash flood warnings for canyons west of the Denver metro area.
The floods are the worst to hit Colorado for more than 30 years, and have prompted President Barack Obama to approve a federal disaster assistance request.