It could be several more days before electricity is restored to areas hit by vicious storms that killed at least 13 people and left 3 million power customers to negotiate sweltering temperatures without air conditioning.

Across a swath from Indiana to New Jersey and south to Virginia, officials warned the heat wave could take a toll on the elderly, young or sick. Problems from the storms that began Friday ranged from a damaged prison in Illinois to tree-strewn train tracks that stranded 232 Amtrak passengers for more than 20 hours in West Virginia.

Emergencies have been 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.

Maryland Gov. Martin O'Malley said utility crews were working to untangle downed tree limbs and power lines. The fact these storms were so unexpected has added to the challenge. Crews are traveling from as far away as Florida and Texas to help, O'Malley said Sunday on CNN's "State of the Union."

"Unlike a polite hurricane that gives you three days of warning, this storm gave us all the impact of a hurricane without the warning of a hurricane," he said.

Power officials said the outages wouldn't be repaired for several days to a week.

The bulk of the storm damage was in West Virginia, Washington and the capital's Virginia and Maryland suburbs. At least six of the dead were killed in Virginia, including a 90-year-old woman asleep in her 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.

In Washington's northern Virginia suburbs, emergency 911 call centers were out of service; residents were told to call local police and fire departments. Huge trees toppled across streets in the nation's capital, crumpling cars. Cellphone and Internet service was spotty, gas stations shut down and residents were urged to conserve water.

The power outages were especially dangerous because they left the region without air conditioning in an oppressive heat wave. Temperatures soared to highs in the mid-90s Saturday in Baltimore and Washington, a day after readings of up to 104 degrees were reported in the region. Yet another day of temperatures reaching 100 degrees was forecast for much of the region Sunday.

Three Baltimore City fire companies set to permanently close this week were staying open several more days to help cope.

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 destruction. Winds and toppled trees brought down entire power lines, and debris has to be cleared from power stations and other structures.

New Jersey Gov. Chris Christie ordered the National Guard to deliver fuel for generators and fresh water to stricken areas. He reported that power had been restored to such tourist areas as Atlantic City's casinos.

Illinois corrections officials transferred 78 inmates from a prison in Dixon to the Pontiac Correctional Center after storms Friday night caused significant damage in the state, Department of Corrections spokeswoman Stacey Solano said.

No one was injured, Solano said. Generators are providing power to the prison, which is locked down, confining remaining inmates to their cells.

In West Virginia, 232 Amtrak passengers were stranded Friday night on a train blocked on both sides of the tracks by toppled trees.

Brooke Richart, a 26-year-old teacher from New York City, was among the passengers stranded for 20 hours. She read half a book and took walks outside the train, which had light, air conditioning and food the entire time. But she called the wait "trying."

"Thankfully we could go in and out of the train because we were there so long. If you wanted to stretch your legs or take a walk, you could," she said.

Amtrak spokesman Steve Kulm said passengers were taken away by buses Saturday night.

Some major online services also saw delays and disruptions.

Netflix, Instagram and Pinterest resorted to using Twitter and Facebook to update subscribers after violent storms across the eastern U.S. caused server outages for hours. Netflix and Pinterest restored service by Saturday afternoon.

Instagram used its Facebook fan page to communicate with users of its photo-sharing service. It posted a message on Saturday morning that blamed the electrical storm for the outage that sent its engineers scrambling to restore service.

Meanwhile, utilities said they were struggling to restore power amid the heat wave.

"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," said Myra Oppel, a spokeswoman for the utility Pepco, which serves Washington and its suburbs.

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, David Gunnoe, uses a wheelchair and had to spend the night in the community room of his apartment complex because the power _ and his elevator _ went out. Rescuers went up five floors to retrieve his medication.

Others sought refuge in shopping malls, movie theaters and other places where the air conditioning would be cranked up. Others simply tried to make the best of a bad situation.

In the Columbus, Ohio, suburb of Dublin, Lori Schaffert said her household borrowed a generator from a friend and was alternating it between the refrigerator and freezer while using flashlights and battery-operated lanterns for light. Her 5-year-old daughter and a neighbor friend played board games and helped her make pickles from their garden's cucumbers.

"You come to appreciate the simple life a little more in these times," Schaffert said.

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Associated Press writers Vicki Smith in Morgantown, W.Va.; Larry O'Dell in Richmond, Va.; Pam Ramsey in Charleston, W.Va.; Jonathan Drew in Atlanta; Dan Sewell in Cincinnati; Doug Ferguson in Bethesda, Md.; and Rebecca Miller in Philadelphia contributed to this report.