Colorado towns already crumbling under the weight of historic flooding got pounded again Sunday with sometimes torrential downpours as the flood death toll and the number of people still unaccounted for continued to rise.

Up to 4 inches of rain fell in parts of Larimer County, where authorities said an 80-year-old woman went missing and is presumed dead, bringing the total of people killed to six since flooding began Wednesday evening. The forecast called for more rain Monday.

As flooding along the South Platte River moved downstream into northeast Colorado, communities braced for unprecedented rising water levels.

Emergency management officials said 17,494 homes were damaged, 1,502 homes were destroyed and 11,700 people were ordered evacuated.

As of Sunday, rescuers had evacuated more than 2,100 people and more than 500 pets, most by helicopter

“The situation has deteriorated,” Boulder County Emergency Management spokesman Andrew Barth said Sunday. “There’s a heavy, heavy fog, and rain is coming down hard.”

The flooding has been catastrophic for dozens of Front Range and Eastern Plains towns and cities.

Hundreds of local and federal rescuers crisscrossed remote slopes on foot and in ATVs trying to find people who have not been heard from in days.

Even as rescuers found stranded people and crossed them off the list of “the unaccounted for,” that list continued to grow as more people called police asking for welfare checks on friends and relatives they couldn’t reach.

The list across the state now tallies 1,253 people unaccounted for. The fear is that some of them are dead, Barth said.

On Sunday, federal aid continued flowing into the state.

The Federal Emergency Management Agency deployed two Incident Management Assistance Teams and staff for Colorado emergency operations centers.

Three federal urban search-and-rescue teams — Colorado Task Force 1, Utah Task Force 1 and Nebraska Task Force 1 — also were rescuing people in storm-damaged areas. Two more teams are expected Monday.

FEMA is providing more than 65,000 liters of water and 22,000 meals. A FEMA communications vehicle is assisting in operations in Lyons.

President Barack Obama called Gov. John Hickenlooper on Sunday to reiterate his commitment to providing federal support, according to a White House news release.

Obama declared a major disaster in Colorado on Saturday, authorizing federal funds for flood victims.

FEMA Administrator Craig Fugate will travel to Colorado on Monday to help coordinate the federal response.

Nevertheless, Sunday saw another day of drenching rain and heart-wrenching stories.

In the Cedar Cove area of Big Thompson Canyon, an injured 80-year-old woman could not leave her house, said Larimer County sheriff’s spokesman John Schulz. “When people came back to help her, the house was gone,” he said.

It was the second day in a row that a woman was reported missing and presumed dead in the Cedar Cove area. A 60-year-old woman was reported missing Saturday.

Overflowing streams and rivers forced the state Department of Transportation to shut down Interstate 25 from Colorado 7 to Colorado 52 in both directions.

Municipal officials issued new evacuation orders to residents in Longmont, Greeley, Weld County and Estes Park.

Pouring rain west of Longmont triggered re-evacuations of the Greens, Champion Greens and the Valley neighborhoods.

Neighborhoods south of Colorado 119 near I-25 also were ordered to leave as Mountain View Fire and Rescue reported the St. Vrain River was rising 7 inches every 15 minutes Sunday morning.

Flooding has wiped away large sections of roads, making it risky or impossible to reach people in dangerous areas and slowing rescue efforts, Barth said.

Fifteen helicopters in Boulder County that evacuated 1,200 people from Lyons and 295 people from Jamestown were grounded Sunday because of low visibility, Barth said.

Sixteen helicopters in Larimer County were grounded Sunday.

Authorities across the flooded areas warned that it could take many months before infrastructure, including new roads, will be completed.

Xcel Energy officials said Sunday they will have to replace thousands of natural-gas meters and up to 20 miles of natural-gas pipeline. More than 4,000 customers are without gas in Boulder County, according to the utility.

National Guard and Boulder County heavy-equipment operators began to rebuild creek and river banks after floodwaters created new waterways that have swamped several communities.

“We’re going to try to divert the St. Vrain River back into its original channel,” Barth said.

It could take several months to rebuild the banks so that the river flows down its original channel, Barth said.

Crews also have been repairing and rebuilding roads to reach isolated mountain communities, including Lyons and James-town.

“We did punch a hole getting to Jamestown, but its still pretty slippery,” Barth said.

Near Hillrose in northeast Colorado, BNSF Railway workers were dumping loads of gravel in an attempt to reinforce the railroad bed as the South Platte River widened to within 6 feet of the track. The line is used to move coal from Wyoming to a power plant near Brush.

Some residents in the area said the river’s surge is bigger than what they saw in 1965, when flooding along the Front Range and Eastern Plains left 21 dead and 250,000 acres inundated.

Flooding in the Denver metro area was severe in 1965. A storm surge destroyed 120 houses and damaged 935 in Littleton, Englewood and Denver. Also, 280 mobile homes were lost, and 16 bridges in Denver were demolished. After the flood, Chatfield and Bear Creek reservoirs were built to control storm waters.