Millions across the mid-Atlantic region had to swelter in the aftermath of violent storms that pummelled the eastern US with high winds and downed trees, killing at least 13 people and leaving 3 million without power during a 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 Governer 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.
In West Virginia, 232 Amtrak passengers spent Friday night on a train that was blocked on both sides by trees that fell on the tracks, and they were waiting for buses to pick them up on Saturday.
In Illinois, storm damage forced the transfer of dozens of maximum-security, mentally ill prisoners from one prison to another.
In some Virginia suburbs of Washington, emergency call centres 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.
Cell phone 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 highs in the mid-90s in Baltimore and Washington, where it had hit 104 (40 Celsius) on Friday.
"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.
Last night, the train passengers stranded near rural Prince, West Virginia, were loaded into buses after they got stuck at 11 pm the previous evening, said Amtrak spokesman Steve Kulm.
Kulm said the train bound from New York to Chicago had power, so lights and air conditioning were working. He said that since it's a long-distance train, it was stocked with food and crew members were able to get to town to buy more.