Three more people were confirmed Monday to have been killed in Colorado's disastrous flooding, raising the death toll to eight as the largest civilian helicopter mission since Hurricane Katrina scoured the state in hope of reaching hundreds of people still stranded.
A spokeswoman for the state Office of Emergency Management told NBC News that the eighth person died Monday afternoon in Clear Creek County. She had no further details, but The Denver Post, quoting police in the town of Idaho Springs, reported that an 83-year-old man was swept away when the ground gave way near where he was standing. The man's body was found three miles downstream.
At least 648 other people remain unaccounted for, the state Office of Emergency Management reported Monday night. Search-and-rescue teams from Utah, Nebraska, Nevada, California and Missouri have converged on the state to try to find them.
Gov. John Hickenlooper told reporters that saving lives was the top priority, adding that 21 helicopters were helping with the searches while officials of the Federal Emergency Management Agency scrambled to help flood-hit families and individuals.
More than half of those missing, 398, were in Larimer County, scene of some of the heaviest devastation. Across the Front Range — the Rocky Mountain region that is home to Denver, Boulder, Colorado Springs and several of the state's other largest municipalities — about 1,500 homes have been destroyed and almost 18,000 others have been damaged, emergency officials said.
Two people were missing and presumed dead in Larimer County, near the Wyoming line, the county sheriff's office. Sixteen helicopters from the National Guard and other agencies were on standby after parts of the county were hit with what meteorologists called a "1,000-year flood" — a deluge of such scope that it has only a 0.1 percent chance of happening in any particular year.
"I'm hopeful that the vast majority of these people are safe and sound," Hickenlooper said on NBC's TODAY. "But we do not have any illusions that there could well be more casualties."
Authorities also dispatched helicopters to rescue an unknown number of people stranded in Jamestown, a northwest Boulder County town of fewer than 300 residents that was left virtually unreachable after floodwaters swallowed huge swaths of the primary access road, said Nick Grossman, a spokesman for the county's office of emergency management.
Jamestown is "essentially an island right now," Grossman said.
Officials instructed isolated people in other hard-hit mountain towns to set flares, wave light-colored sheets from the roofs of houses and use mirrors to reflect the sunlight to attract the attention of the teams sent to save them.
In Boulder County, closer to Denver, crews were going house to house looking for stranded people. The Army and the National Guard had rescued at least 1,750 people cut off by washed-out roads in the mountain canyons, an Army spokesman said.
Forecasters said the rain would probably taper off Monday, but the weather presented another challenge — fog. Ten military helicopters couldn't take off from Boulder Municipal Airport until late Monday morning after having been grounded.
On Sunday, authorities added 12 counties to a presidential disaster declaration, increasing the total to 15. Federal officials provided food, water, cots and generators, bolstering the state and local response.
People in the 15 counties can also apply for help from FEMA. Those counties cover 4 million people.
Separately, President Barack Obama on Saturday declared a major disaster for Boulder County. That step makes it easier for flood victims to get help for temporary housing and low-cost loans to cover uninsured property losses.
Alexander Smith, Brinley Bruton, Daniel Arkin, Elisha Fieldstadt and Steven Louie of NBC News contributed to this report.