Authorities said Saturday they were concerned the additional rain would bring more flooding to the region where at least 272 people could not be contacted by relatives and friends, CNN reported. There was also concern the new rains might trigger mudslides.
The National Weather Service said 1.73 inches of rainfall was recorded within a span of 30 minutes in southeast Denver, and the forecast called for thunderstorms in the area Saturday night with more rain Sunday, CNN reported.
A 60-year-old woman whose name was not reported was presumed dead after she was swept away by floodwater that destroyed her home. Larimer County Sheriff's Office Executive Officer Nick Christensen said neighbors had tried to rescue the woman before she was swept away.
Boulder County Sheriff Joe Pelle told the Boulder Daily Camera searchers assume some of the missing have been stranded but he assumes "there may be further loss of life or injuries."
"The things that worry us are what we don't know," he said. "We don't know how many lives are lost, we don't know about homes lost."
Officials said many of those unaccounted for were probably safe, but did not have telephone service.
"These are people whose family or friends haven't been able to reach or account for them, not necessarily in harm or dire need," said county spokeswoman Gabrielle Boerkircher.
Roads and bridges were either washed out or in jeopardy from the fast-moving water. Communications and other utilities were also problematic.
The National Guard and Federal Emergency Management Agency teams were on the scene, and the mayor of Boulder ordered residents not to explore flooded areas in boats or flotation devices, CNN said.
Larimer County Sheriff John Schulz said Friday it appeared the flood waters had crested and would recede Saturday despite additional rain in the forecast.
"We hope the worst has passed," he told CNN.
Colorado Gov. John Hickenlooper said damage from the flooding "is not going to get fixed in a week."
"We have lost a great deal of infrastructure," he said.
Hickenlooper said on his Twitter account the helicopter carrying him for an inspection of the affected area picked up a total of six stranded people, a dog and a cat at two locations Saturday afternoon.