MONTPELIER, Vt. (AP) -- The storm that had been Hurricane Irene crossed into Canada overnight but wasn't yet through with the U.S., where flood waters threatened Vermont towns and big city commuters had to make do with slowly reawakening transit systems.

The storm left millions without power across much of the Eastern Seaboard, killed at least two dozen and forced airlines to cancel about 9,000 flights. It never became the big-city nightmare forecasters and public officials had warned about, but it caused the worst flooding in a century in Vermont.

Many of the worst effects arose from rains that fell inland, not the highly anticipated storm surge along the coasts. Residents of Pennsylvania and New Jersey nervously watched waters rise as hours' worth of rain funneled into rivers and creeks. Normally narrow ribbons of water turned into raging torrents in Vermont and upstate New York late Sunday, tumbling with tree limbs, cars and parts of bridges. 

"This is not over," President Barack Obama said from the Rose Garden.

Hundreds of Vermonters were told to leave their homes after Irene dumped several inches of rain on the landlocked state. Gov. Peter Shumlin called it the worst flooding in a century, and the state was declared a federal disaster area.

"We prepared for the worst and we got the worst in central and southern Vermont," Shumlin said Monday. "We have extraordinary infrastructure damage," including communities that were cut off, hundreds of roads closures and the loss of at least three historic covered bridges.

Video posted on Facebook showed a 141-year-old covered bridge in Rockingham, Vt., swept away by the roiling, muddy Williams River. In another video, an empty car somersaulted down a river in Bennington.

"It's pretty fierce. I've never seen anything like it," said Michelle Guevin, who spoke from a Brattleboro restaurant after leaving her home in nearby Newfane. She said the fast-moving Rock River was washing out the road to her house.

Officials at one point thought they might have to flood the state capital, Montpelier, to relieve pressure on a dam. But by Monday morning that threat had abated.

Nearly 5 million homes and businesses lost power at some point during the storm. Lights started to come back on for many on Sunday, though it was expected to take days for electricity to be fully restored.

Only about 50,000 power customers in New York City went dark, but people there had something else to worry about: getting to work Monday.

The metropolitan area's transit system, shut down because of weather for the first time in its history, was taking many hours to get back on line. Limited bus service began Sunday and New York subway service was partially restored at 6 a.m. Monday.

Commuter rail service to Long Island and New Jersey was being partially restored, but the Metro-North Railroad to Westchester County and Connecticut was suspended because of flooding and mudslides.

Riders were warned to expect long lines and long waits, but early commuters reported empty subways and smooth rides.

Mentor Vargas, 54, said he made his 40-minute trip on the J train without incident. "It seems people aren't going to work today," he said on his way to work at a repair company in Queens.

Likewise, Philadelphia's transit system was mostly restarted Monday, though some train lines weren't running because of downed trees and wire damage.

Airports in New York and around the Northeast reopened to a backlog of hundreds of thousands of passengers whose flights were canceled over the weekend.

Some of New York's yellow cabs were up to their wheel wells in water, and water rushed over a marina near the New York Mercantile Exchange, where gold and oil are traded. But the New York flooding was not extensive from Irene, whose eye passed over Coney Island and Central Park.

The New York Stock Exchange was opening for business on Monday, and the Sept. 11 memorial at the World Trade Center site didn't lose a single tree.

Mayor Michael Bloomberg defended his decision to order 370,000 residents to evacuate their homes in low-lying areas, saying it was impossible to know just how powerful the storm would be. "We were just unwilling to risk the life of a single New Yorker," he said.

Irene had at one time been a major hurricane, with winds higher than 110 mph as it headed toward the U.S. It was a tropical storm with 65 mph winds by the time it hit New York. It lost the characteristics of a tropical storm and had slowed to 50 mph by the time it reached Canada.

Chris Fogarty, director of the Canadian Hurricane Centre, warned of flooding and wind damage in eastern Canada and said the heaviest rainfall was expected in Quebec, where about 250,000 homes were without power.

At least 25 people died in the U.S., most of them when trees crashed through roofs or onto cars. One Vermont woman was swept away and feared drowned in the Deerfield River.

Officials worked to repair hundreds of damaged roads, and power companies picked through uprooted trees and reconnected lines.

One private estimate put damage along the coast at $7 billion, far from any record for a natural disaster.

Twenty homes on Long Island Sound in Connecticut were destroyed by churning surf. The torrential rain chased hundreds of people in upstate New York from their homes and closed 137 miles of the state's main highway.

Authorities in and around Easton, Pa., kept a close eye on the rising Delaware River. The National Weather Service forecast the river to crest there at more than 27 feet, about 5 feet above flood stage.

In the South, authorities still were not sure how much damage had been done but expressed relief that it wasn't worse.

"Thank God it weakened a little bit," said Virginia Gov. Bob McDonnell, who toured a hard-hit Richmond neighborhood where large, old-growth trees uprooted and crushed houses and automobiles.

In Norfolk, Va., where storm surges got within inches of breaking a record, most of the water had receded by Sunday. There was isolated flooding and downed trees, but nowhere near the damage officials predicted.

"We can't believe a hurricane came through here," city spokeswoman Lori Crouch said.

In North Carolina, where six people were killed, the infrastructure losses included the only road to the seven villages on Hatteras Island.

"Overall, the destruction is not as severe as I was worried it might be, but there is still lots and lots of destruction and people's lives are turned upside down," Gov. Beverly Perdue said in Kill Devil Hills.

In an early estimate, consulting firm Kinetic Analysis Corp. figured total losses from the storm at $7 billion, with insured losses of $2 billion to $3 billion. The storm will take a bite out of Labor Day tourist business from the Outer Banks to the Jersey Shore to Cape Cod.

Irene was the first hurricane to make landfall in the continental United States since 2008, and came almost six years to the day after Katrina ravaged New Orleans on Aug. 29, 2005.

Contributing to this report were Associated Press writers Samantha Gross, Beth Fouhy, Samantha Bomkamp, Verena Dobnik, Jonathan Fahey, Tom Hays, Colleen Long and Larry Neumeister in New York; Brock Vergakis in Virginia Beach, Va.; Marc Levy in Chester, Pa. and Jeff McMillan in Philadelphia; and Seth Borenstein and Christopher S. Rugaber in Washington.

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