More than 500 people still unaccounted for in deadly Colorado floods

More than 500 people remained unaccounted for Sunday across areas of Colorado after deadly flash floods swept through, destroying homes and taking at least four lives.

About 350 of those are in Larimer County where officials haven't yet counted them as missing though they have not contacted family members.

A Dallas man told The Coloradoan newspaper that he saw a photo of his mother's house in ruins on a Denver TV station.

"I don't know that she's even OK," Rob Clements told the newspaper about his 73-year-old mother, Libby Orr, who he last spoke with Thursday before phone service cut off.

"I presume she is. But her house, if not completely gone, fell into the river and is most of the way gone."

Another round of storms is expected to dump more rain on the flood ravaged area on Sunday.

Thousands of residents have evacuated their homes since the floodwaters rushed in overnight on Wednesday.

Four people have so far been confirmed dead. 

Larimer County Sheriff's office said in a tweet that a fifth victim, "a 60-year-old woman from Cedar Grove … is missing and presumed dead."

Witnesses saw floodwaters destroy the woman's home in the Cedar Cove area, Sheriff's office spokesman John Schultz said.

"We're sure there are going to be additional homes that have been destroyed, but we won't know that for a while," Schulz said.

"I expect that we're going to continue to receive reports of confirmed missing and confirmed fatalities throughout the next several days."

National Guard helicopters joined hundreds of troops to search the remote, mountainous terrain for residents who have been cut off for days.

Evacuations are still being called for the areas around the flood zone and officials warn it will be difficult to rescue anyone who refuses the order.

"It is a sinking feeling when you realize that when some people call … we are not going to be able to get to them," Boulder County Sheriff Joe Pelle said. "But we are making great progress."

Residents who don't evacuate can expect to spend an uncomfortable few weeks without power, cellphone service or water.

"Essentially, what they were threatening us with is, 'If you stay here, you may be here for a month,'" 79-year-old Dean Hollenbaugh, who was evacuated by helicopter from Jamestown, northwest of Boulder, told CBS News.

The National Weather Service in Boulder said that new round of showers and thunderstorms lasting into Sunday could trigger more flash floods.

Some parts of Colorado that normally sees less than 2 inches of rain in all of September have been flooded with more than 14 inches in a week.

"We're going to be in for some steady rain over the next 12 hours," Kim Kobel, a spokesperson for Boulder's Office of Emergency Management told CNN.

The extra rain shouldn't total more than 1 to 2 inches though. "So that's the good news," Kobel said.