RICHMOND, Va. (AP) — Gov. Bob McDonnell declared a state of emergency Saturday after a powerful storm killed six people in the state and knocked out power for hundreds of thousands, leaving them without air-conditioning in the middle of a blistering heat wave.

"This is a very dangerous situation for Virginia," McDonnell said at a news conference at the state's Emergency Operations Center. He said the threat of more storms, continued extreme heat and the largest non-hurricane power outage in state history — and fifth largest ever — could mean a few more days of misery.

McDonnell urged Virginians to look out for their neighbors, especially elderly people who are more vulnerable to heat-related illnesses.

"Be your neighbor's keeper," he said.

The governor's emergency declaration activated 300 National Guard troops to help the state recover from straight-line winds of up to 80 miles an hour that felled trees and power lines and closed about 250 secondary roads.

Fairfax County police said trees blown down by heavy winds killed one person in a car and a 90-year-old woman sleeping in her bed. In Albemarle County, police said 64-year-old John Porter was killed by a falling tree outside his house and Catherine Ford was killed when she got out of her car, which was blocked by fallen trees, and was hit by another toppled tree.

The Bedford County Sheriff's Office said an elderly couple died in a fire that appears to have been caused by the storm.

About 769,500 customers of Appalachian Power and Dominion remained without service late Saturday afternoon. That was down from a peak of more than 1.2 million earlier in the day.

Rodney Blevins of utility giant Dominion said it was unclear how long it will take to get power fully restored but added that Virginians should "anticipate long outages."

Tracey Phalen of Richmond could relate to that advice. After enduring six days without electricity because of Hurricane Irene last summer, she was bracing for another uncomfortable stretch because of the latest storm-related outage.

"I think it's going to get bad," she said as she and her teenage son relaxed under the shade of a coffee-house umbrella. "But I always tend to think there are a lot of people who have it worse."

She said her family would find someplace cool to get through the day.

"We'll probably go to a movie theater at the top of the day," she said.

Dozens of schools, fire stations and community centers were opened across the state as cooling centers, but many Virginians found other ways to avoid the heat.

Brett Shiflett of Richmond said she would be staying with various family members in the area after the storm sent a tree crashing into the apartment above hers, cutting off power and leaving her kitchen a soggy shambles.

"I'm going to be house-hopping for a while," she said.

The huge tree wiped out the rear portion of the upstairs apartment. A bed with a broken headboard was covered with debris was a tangled mess of bricks and lumber from what used to be a deck.

Had the storm hit later, David Fetchko's girlfriend might have been sleeping in that bed.

"She probably would have been killed," said Fetchko, who relayed a message from his girlfriend that she was still too shaken to talk about the ordeal.

Shiflett was home when the tree fell.

"It sounded like an earthquake and like someone upstairs fell really hard," she said. Then it started raining in her kitchen, which is directly below her neighbor's demolished bedroom.

"It's a little traumatizing," she said.

Others in the city also were cleaning up after the storm and contemplating how they were going to cope with the relentless heat.

"I'm heading to the river to sit in the water with the dog," Tricia Pearsall said as she swept up fallen tree branches in front of her 170-year-old home downtown. "We're lucky to have air-conditioning, but I'd rather be in the river."

Ramel Lloyd was waiting for a friend to come over with a nail gun to reattach four sections of privacy fencing that were flattened at the home he just bought three weeks ago. The storm also ripped off a small section of siding, and a power surge apparently caused a ceiling fan to catch fire.

"Luckily, everyone is safe," he said. "It was an eventful 12 hours, to say the least."

Around the corner from Lloyd's house, a large tree crushed two cars, including Greg Hough's compact wagon.

"It's totaled," Hough said. "The golf clubs are OK though."