WASHINGTON — Millions across the mid-Atlantic region sweltered Saturday in the aftermath of violent storms that pummeled the eastern U.S. with high winds and downed trees, killing at least 13 people and leaving 3 million without power during a triple-digit heat wave.

Power officials said the outages wouldn’t be repaired for several days to a week, likening the damage to a serious hurricane. Emergencies were declared in Maryland, West Virginia, Ohio, the District of Columbia and Virginia, where Gov. Bob McDonnell said the state had its largest non-hurricane outage in history, as more storms threatened. “This is a very dangerous situation,” the governor said.

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A brick wall collapsed in Columbus Grove, Ohio, on Friday after a series of thunderstorms brought heavy winds. The Associated Press

In some Virginia suburbs of Washington, emergency 911 call centers were out of service; residents were told to call local police and fire departments. Huge trees fell across streets in Washington, leaving cars crunched up next to them, and onto the fairway at the AT&T National golf tournament in Maryland.

Cellphone and Internet service was spotty, gas stations shut down and residents were urged to conserve water until sewage plants returned to power.

The outages were especially dangerous because they left the region without air conditioning in an oppressive heat. Temperatures soared to the mid-90s by mid-afternoon along the southeast coast and pushed to over 100 degrees inland.

“I’ve called everybody except for the state police to try to get power going,” said Karen Fryer, resident services director at two assisted living facilities in Washington.

The facilities had generator power, but needed to go out for portable air conditioning units, and Fryer worried about a few of her 100 residents who needed backup power for portable oxygen.

More than 200 miles away in Morgantown, W.Va., Jeff and Alice Haney loaded their cart at Lowe’s with cases of water, extra flashlights and batteries, and wiring for the generator they hoped would be enough to kick-start their air conditioner. Even if they had to live without cool air, the family had a backup plan.

“We have a pool,” Jeff Haney said, “so we’ll be OK.”

The storm did damage from Indiana to New Jersey, although the bulk of it was in West Virginia, Washington and suburban Virginia and Maryland.

At least six of the dead were killed in Virginia, including a 90-year-old woman asleep in bed when a tree slammed into her home. Two young cousins in New Jersey were killed when a tree fell on their tent while camping. Two were killed in Maryland, one in Ohio, one in Kentucky and one in Washington.

Utility officials said it could take at least several days to restore power to all customers because of the sheer magnitude of the outages and the destruction. Winds and toppled trees brought down entire power lines, and debris has to be cleared from power stations and other structures. All of that takes time.

“This is very unfortunate timing,” said Myra Oppel, a spokeswoman for Pepco, which reported more than 400,000 outages in Washington and its suburbs. “We do understand the hardship that this brings, especially with the heat as intense at is. We will be working around the clock until we get the last customer on.”

Especially at risk were children, the sick and the elderly. In Charleston, W.Va., firefighters helped several people using walkers and wheelchairs get to emergency shelters. One of them, Steve Gunnoe, who uses a wheelchair and had to spend the night in the community room of his apartment complex.

Gunnoe said he was grateful for the air conditioning, but hoped power would be restored soon.

“It doesn’t matter if it’s under a rock some place. When you get used to a place, it’s home,” he said.

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