(Updates unaccounted total, adds disaster declarations in Colorado and New Mexico, details)
By Keith Coffman
BOULDER, Colo., Sept 13 (Reuters) - National Guard troops plucked stranded residents out of danger by helicopter and hauled them out of an inundated community in military trucks on Friday as the death toll from the worst floods to hit Colorado in decades rose to four with 172 people still unaccounted for.
Taking advantage of a break in torrential rains that have unleashed floodwaters up and down the state, Guard members rumbled into the hard-hit town of Lyons through waist-high water and went door to door to pull out up to 2,000 trapped residents.
"These individuals are not only coming with just themselves, but with their suitcases and their precious household items along with their pets and everything, all getting loaded in the back of these vehicles," said First Lieutenant Skye Robinson, a spokesman for the Colorado National Guard.
Elsewhere in the state, search and rescue teams used helicopters to hoist some 200 residents to safety one by one by hovering over flooded areas because there was no place to land after raging waters washed out roads and inundated farmland.
The flooding - so intense it toppled buildings in some places - began overnight Wednesday. It was triggered by unusually heavy late-summer storms that drenched Colorado's biggest urban centers, from Fort Collins near the Wyoming border south through Boulder, Denver and Colorado Springs.
Boulder and a string of other towns along the Front Range of the Rockies north of Denver were especially hard hit as water poured down rain-soaked mountains and spilled through canyons that funneled the runoff into populated areas.
Lyons, north of Boulder, was virtually cut off when floodwaters washed out U.S. Route 36, and residents have been without water and power for 48 hours, said Mike Banuelos, a spokesman for the Boulder County Emergency Operations Center.
At least four people were killed, including a couple swept away in floodwaters after stopping their car northwest of Boulder. The man's body was recovered on Thursday and the woman had been missing and feared dead before her body was found on Friday.
Also killed were a person whose body was found in a collapsed building near Jamestown, an evacuated enclave north of Boulder, and a man in Colorado Springs, about 100 miles (160 km) to the south, officials said.
On Friday, Governor John Hickenlooper declared a disaster emergency for 14 counties, reaching from the Wyoming border south to Colorado Springs. The declaration authorizes $6 million in funds to pay for flood response and recovery.
In neighboring New Mexico, where floods forced the evacuation of hundreds of people in Eddy, Sierra and San Miguel counties, Governor Susana Martinez declared a state of disaster on Friday making funding available to state emergency officials for recovery efforts.
The Boulder Office of Emergency Management listed 172 people as unaccounted for following the floods, stressing that while they were not yet considered missing or in danger, relatives and authorities had not been able to contact them.
Authorities said many western mountain communities remained isolated with no potable water or working septic systems.
LANDSCAPE COVERED IN BROWN WATER
In rural Weld County, where the South Platte River has overflowed its banks and virtually cut the county in half, aerial TV footage showed large stretches of land covered in brown water. Many homes and farms were largely half-submerged.
Weld County sheriff's spokesman Steve Reams said nearly every road in and around a cluster of towns that includes Greeley, Evans and Milliken had been closed by flooding, including bridges that were washed out.
Rescue teams were evacuating some stranded residents by boat, while some farmers managed to move to high ground on their tractors, Reams said in an interview with the Denver-area ABC television affiliate.
The flooding was the worst in the state since nearly 150 people were killed near Boulder in 1976 by a flash flood along the Big Thompson Canyon.
The size and scope of property losses remain unquantified, with county assessment teams unlikely to begin preliminary evaluations of the damage at least until early next week, once water has receded, said Micki Frost, spokeswoman for the Colorado Office of Emergency Management.
President Barack Obama approved a federal disaster assistance request, which will release funds to help with emergency protection.
Frost said an unknown number of homes and other structures had collapsed in state but that "we have no structure count at this point" because some areas are still under water.
Hickenlooper said evacuations were the highest priority and advised people to stay out of debris- and sand-filled floodwaters that were "almost like liquid cement."
"It's got to be the largest storm that I can imagine in the state's history," he told a televised news conference.
In Boulder, the storms shattered a September rainfall record set in 1940, officials said, unleashing surging floodwaters in Boulder Canyon above the city that triggered the evacuation of some 4,000 residents late on Thursday.
Also on Friday, flooding forced the Colorado Department of Transportation to shut down a 70-mile (112 km) stretch of Interstate 25 from north of Denver to the Wyoming border, said agency spokeswoman Mindy Crane.
Boulder Creek, which runs through the heart of Boulder, became a raging torrent that burst its banks and flooded adjacent parking lots and streets as warning sirens wailed.
The National Weather Service said at least 14.7 inches (37.4 cm) of rain have fallen on Boulder this month, smashing a 73-year-old record of 5.5 inches (14 cm) for September.
In Longmont, about 14 miles (22 km) northeast of Boulder, the St. Vrain River jumped its banks, cascading across main thoroughfares and cutting the city in two. Assistant city manager Shawn Lewis said 7,000 households were under mandatory evacuation orders. (Additional reporting by Steve Gorman, Alex Dobuzinskis and Dan Whitcomb; Writing by Dan Whitcomb; Editing by Cynthia Johnston and Bill Trott)