Tens of thousands of people remained without power in the Pacific Northwest after a winter storm blanketed the region with ice and snow and made travel treacherous.

The greater Portland, Oregon, area was the hardest hit, with more than 200,000 people still without power today. Authorities said it could be a day or more before electricity is fully restored, and forecasters warned of more hazardous weather through Monday.

With a number of transmission lines and substations knocked out of service and ice and wind still threatening to bring down tree limbs, some people could experience multiple outages or prolonged outages, said Steve Corson, a spokesperson for PGE, one of the area’s major electricity providers.

“Our hope would be that most would be restored sooner than that, but some customers will be affected for several days,” he said.

The utility, which had over 250,000 customers without power on Saturday, is bringing in crews from Nevada and Montana to help restore power, he said.

The extreme conditions, loss of power and transportation problems prompted Oregon Gov. Kate Brown to declare a state of emergency for the greater metro area Saturday.

“Crews are out in full force now and are coordinating with local emergency response teams on communications for emergency services, such as warming centers,” Brown said in a statement. “I’m committed to making state resources available to ensure crews have the resources they need on the ground.”

Winter storms and extreme cold affected much of the U.S. West, particularly endangering homeless communities. Volunteers and shelter staffers were trying to ensure homeless residents in Casper, Wyoming, were indoors as the National Weather Service warned of wind chill reaching as much as 35 degrees below zero over the weekend. Authorities in western Washington and western Oregon opened warming shelters in an effort to protect homeless residents from the wet and cold.

In the Portland area, many ice-laden trees snapped under the weight, falling on power lines and causing transformers to blow out in showers of blue and orange sparks.

Brian Zevenbergen watched Saturday as a crew sawed up two large, ice-covered trees that had crashed across his driveway overnight, narrowly missing two cars parked there. His house in Lake Owego had also lost power overnight. Just around the corner, another massive tree blocked the street in the suburb south of Portland and had taken out a city street light.

“Last night, everything was standing, and this morning the two trees had me blocked in the driveway and were blocking at least half the street,” he said. “Friends on the lower levels have power, so I have invites to go hang out there.”

The ice and snowfall caused treacherous driving conditions, forcing Oregon transportation officials to close Interstate 84 in the Columbia River Gorge, and the regional transit agency TriMet suspended all bus and train service in the region.

TriMet spokesperson Tia York asked people to avoid all travel unless it’s an emergency. “It is too dangerous out there,” York wrote in a statement.

Police in Salem, Oregon, also warned residents in Marion and Polk counties to watch for downed power lines and falling tree limbs, and the Oregon State Police said fallen trees blocked several roads across the region.

Some Washington state residents were also socked in by the weather, with snow falling throughout the Seattle region Saturday and freezing rain falling along the coast in Grays Harbor County. The city of Seattle activated its Emergency Operations Center Saturday morning to coordinate the city’s winter storm response.

The Washington State Patrol reported a large accident on Interstate 90 east of Seattle involving 15 collisions. Three vehicles rolled over, but apparently there were no serious injuries.

Heavy snowfall also led to dangerous driving conditions in parts of eastern Oregon and southwestern Idaho, with Malheur County, Oregon, and Boise, Idaho, expected to get as much as 6 inches of snow by Saturday afternoon.

The National Weather Service said all three states should brace for another surge of winter moisture to hit Sunday night, potentially leading to more heavy snowfall through Monday. The “unsettled winter conditions” would likely continue throughout the week, the National Weather Service said Saturday morning.

Western Washington was expected to get an additional 3 to 6 inches of snow on Saturday, with another 2 inches possible today and Monday. Rain falling on accumulated snow raised the possibility of urban flooding happening tonight or Monday in some areas, according to the National Weather Service.

The heavy snow made for dangerous avalanche conditions in the many areas across the Olympics and Cascades mountain ranges, with large avalanches possible. Officials with the Payette Avalanche Center in west-central Idaho also warned of increasing avalanche risk in the days ahead.

Idaho’s neighbors to the east were blasted by brutally frigid weather, with the National Weather Service warning of dangerous wind chills in Montana and Wyoming. The wind chills were expected to reach as low as 50 degrees below zero in Billings, Montana.