President Barack Obama signed an emergency order Thursday night, approving federal disaster aid for Boulder County after torrential rainfall prompted 100-year flooding that has, so far, resulted in two confirmed deaths, at least nine more missing and National Guard rescue efforts.

Continued flooding caused dozens more evacuations throughout the county, power outages and the closure of U.S. 36 on Thursday. Parts of most major roads in Boulder were also closed.

Walls of water coming down canyons triggered mudslides and structure collapses and buildings to be swept away — especially in Jamestown and Fourmile Canyon. The city of Boulder issued an emergency declaration allowing officials to seek support from the state and the Federal Emergency Management Agency.

As of late Thursday night, nine people were reported missing in Boulder, with their family members or friends unable to locate them. More than 400 officers throughout the county were performing search and rescue operations, said Gabrielle Boerkircher, a county spokeswoman.

Officials declined to release the missing persons list for fear citizens would try to go on rogue, dangerous search and rescue missions.

“We’re all pretty much locked in Boulder right now,” Boerkircher said. “The main concern is keeping people off the roads. They need to stay safe at home.”

Crews spent Thursday rescuing stranded people from cars and homes, and they feared the death toll would rise. Sheriff Joe Pelle is pleading with people to stay inside, and non-essential city services, the University of Colorado, Boulder Valley School District, St. Vrain Valley School District and Naropa University will remain closed Friday.

Boulder County Sheriff’s Cmdr. Heidi Prentup said a man died early Thursday morning in the area of Linden Avenue in Boulder County after he got out of his car and tried to rescue a female passenger.

Multiple structures in Jamestown and Fourmile Canyon have collapsed or been swept away, and Boulder County officials confirmed that at least one person was killed in Jamestown after a structure collapse.

Prentup said all sheriff’s deputies are on duty, rotating 12-hour shifts.

“We are still in life-safety mode,” she said.

Emergency officials are still focused on rescue efforts, not damage assessment. They shut down the Boulder Municipal Airport so only emergency personnel can get in to deliver aid, and they have requested helicopters from the National Guard.

Citing safety concerns, they also shut down Boulder’s Open Space and Mountain Parks.

“We have spent the day assisting people stranded in their vehicles, stranded in their homes,” Prentup said.

She said 12 dams in the county have overtopped.

“We don’t have any structural issues with them, but they are over the top of the dams,” Prentup said.

In the city, Linden Avenue — and the nearby Wonderland Hills neighborhood — were among the most severely affected regions, and emergency personnel warned residents Thursday to be ready to evacuate at a moment’s notice.

Robert Reed and his wife, Laurajane, live on South Cedar Brook Road, about 1.5 miles west of Broadway off of Linden Avenue. They evacuated their home on foot Thursday after Cedar Brook was washed out, Reed said.

The couple had two small suitcases, a lock box containing important papers, a handful of other valuables and their dog as they waited at corner of Linden and Broadway for a sheriff’s deputy to drive them to a friend’s house.

“We were prepared to evacuate by car in case of fire,” Reed said. “It never occurred to us there would be a flood.”

Farther west on Linden, Brad MacHamer and his 2 1/2 year-old-son, Mose, watched as a bulldozer moved dirt and debris from the roadway just past Wonderland Hills, clearing the way for other emergency vehicles that were working to slow down water streaming through the neighborhood from the foothills.

MacHamer said he lives near the North Boulder Recreation Center but came to the Wonderland Hills neighborhood to visit friends and observe the flood damage for himself.

“It’s just insane,” he said. “You never think that something like this could happen here.”

In contrast to Wednesday night — when the rain downpours hammered north Boulder — southeast Boulder seemed to take the brunt of the storm Thursday night.

Boulder City Manager Jane Brautigam on Thursday morning signed and issued the local disaster and emergency declaration that allows the city to request support from the state as it responds to the torrential rains and flooding.

Obama declared an emergency in Colorado at about 9:15 p.m., ordering federal aid to supplement state and local response efforts. The action authorizes the Department of Homeland Security and FEMA to coordinate disaster relief efforts in Boulder, El Paso and Larimer counties.

“Specifically, FEMA is authorized to identify, mobilize, and provide at its discretion, equipment and resources necessary to alleviate the impacts of the emergency,” said a news release from the White House.

Boulder Sheriff Joe Pelle said officials feared that more fatalities would be discovered as crews tried to make their way into the mountain towns and heavily affected areas.

“We’re bracing ourselves for the worst,” Pelle said.

With more rain in the forecast, city spokeswoman Sarah Huntley warned Thursday afternoon that “the risk is still very real” and the flood water is dangerous and contains sewage.

Authorities were warning residents of Lyons that it’s unsafe to drink water, and that they need to boil it first or buy bottled water.

As of Thursday, however, drinking water in Boulder was still safe.

Earlier Thursday, people had been ordered to evacuate from Jamestown and Fourmile Canyon.

Pelle said the floodwaters and debris have prevented more crews from reaching the mountain towns.

“All the preparation and want-to in the world can’t put people up the canyon while the debris and water is coming down,” Pelle said. “This is not your ordinary day, this is not your ordinary disaster.”

Boulder has long ranked as one of the state’s top flood hazards and made a national list of six “disasters waiting to happen” published by CU in 2004, along with a devastating hurricane striking New Orleans.

Without a 100-year flood since 1894, the city had said another major flood was “a question of when and not if.”

Check boulderoem.org for updates on evacuations and road closures.

Camera Staff Writers Joe Rubino and Mitchell Byars contributed to this report.