Continuing rainfall hampered Colorado flood rescue efforts even as the death toll rose to six and the number of people unaccounted for increased to 1,300 as of Monday morning. Initial estimates say over 17,000 residential structures have been damaged and about 1,500 destroyed.
"Mother Nature is not cooperating with us today, and currently we are not flying," CNN quoted incident commander Shane Del Grosso as telling reporters in Boulder, one of the two counties worst hit by the flooding that began last Wednesday.
"But tomorrow if we get that window of opportunity, which is sounds like we might get, we have the horsepower to hit it hard," Grosso added.
Rains also prompted authorities to issue fresh flash flood warnings for several northern Colorado communities Sunday.
While authorities had reported four confirmed deaths until Friday, two more people were feared dead during the weekend.
An 80-year-old woman and a 60-year-old woman in Cedar Grove in Larimer, the other worst-hit county, were presumed dead after their separate homes were washed away by the flooding, the county sheriff's office said Sunday.
Earlier, a young couple swept away in floodwaters after they stopped their car northwest of Boulder. In Boulder County's Jamestown, a body was found in a collapsed building. Another man drowned in Fountain Creek in Colorado Springs.
It is being feared that the number of deaths could further rise.
The number of people unaccounted for also rose Sunday to 1,254, USA Today reported, attributing the figure to Micki Trost, a spokeswoman for the Colorado Division of Homeland Security and Emergency Management.
About 500 of those unaccounted for are from Larimer.
"It may be a book-keeping, cross-referencing issue," ABC News quoted Nick Christensen, a spokesman for the Larimer County Sheriff's Office, as saying. "There's been lots of parties that have been evacuated, we've had trouble with phone service and so we have a master list that will get shorter, hopefully far, far shorter, as time goes by and we cross reference and determine where each of those parties are."
Larimer County Sheriff Justin Smith had to fight tears as he described his tour of the county to ABC News on Sunday. "I know exactly inch by inch, mile by mile, community by community, they're taking this stuff back, they're doing it, people are getting those things done out there," he said. "I was devastated by what I saw in there and you had no feel that there was any hope – it felt hopeless in a lot of those areas from the air."
An initial estimate released by the Colorado Office of Emergency Management says about 1,500 homes have been destroyed and about 17,500 have been damaged.
While the actual number of roads damaged or destroyed is unknown, the damage is likely to cost "hundreds of millions" of dollars, Amy Ford, a spokeswoman for the Colorado Department of Transportation, was quoted as saying.
President Barack Obama signed during the weekend a disaster declaration, ordering federal aid for Colorado's Boulder County. Other counties are expected to be added later.
Gov. John Hickenlooper had declared a disaster emergency in 14 counties on Friday, authorizing $6 million to pay for flood response and recovery in Adams, Arapahoe, Boulder, Broomfield, Denver, El Paso, Fremont, Jefferson, Larimer, Logan, Morgan, Pueblo, Washington and Weld, according to Denver Post.