It could be several more days before electricity is restored to areas of the eastern United States hit by storms that killed at least 14 people and left three 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.

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

The death toll inched up to 14 as a spokeswoman for the Virginia State Police said the state medical examiner concluded a traffic death Friday was storm related.

The other deaths all were from falling trees. At least six had been 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.

Maryland's governor says restoring electricity has been a challenge because the storms hit without warning. Gov. Martin O'Malley, speaking on CNN on Sunday, said crews are on their way to help from as far away as Florida and Texas. Utility workers are having to untangle downed tree limbs and power lines, which can be a time-consuming task.

The storm did damage from Indiana to New Jersey, although the bulk of it 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.

No air conditioning amid heat wave

In Washington's northern Virginia suburbs, emergency 911 call centres 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. Cell phone 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.

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.

"The devastation ... is very significant," New Jersey Gov. Chris Christie said after ordering 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 Indiana, a toppled tree crushed the top of Vicki Hunt's car and smashed the back window.

"It came so fast," the Fort Wayne woman told broadcaster WPTA-TV. "All of a sudden all you heard was a swoosh, and next thing you know the tree fell ... we heard a big crash, which obviously was my car."

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

Train passengers stranded

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.

Myra Oppel, a spokeswoman for the utility Pepco, reported over 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, 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 theatres and other places where the air conditioning would be cranked up.

In Richmond, Va., Tracey Phalen relaxed with her teenage son under the shade of a coffee-house umbrella rather than suffer through the stifling heat in a home without power. Phalen said Hurricane Irene left her home dark for six days last summer, "and this is reminiscent of that."

Robert Clements, 28, said he showered by flashlight Friday night after losing power at his Fairfax, Va., home. His fiancee learned electricity wouldn't be restored for days at her apartment complex so she booked a hotel Saturday to beat the heat.

"It feels like an oven," said Clements' fiancée, Ann Marie Tropiano, of the apartment she left behind.

With files from CBC News