Updated

The storm that was once Hurricane Irene crossed into Canada overnight but dangerous floodwaters still threatened communities up and down the East Coast, as residents tried to return home Monday to asses the damage.

The National Hurricane Center said late Sunday that tropical storm warnings are on for the south coast of New Brunswick and Nova Scotia, where Irene was downgraded from a tropical storm, but still packing 50 mph winds.

One private estimate said Irene left up to $7 billion in damages, and millions had been left without power. By Monday morning, the U.S. death toll from the storm had reached 24.

Rivers and creeks turned into raging torrents tumbling with limbs and parts of buildings in northern New England and upstate New York. Flooding was widespread in Vermont, and hundreds of people were told to leave the capital, Montpelier, which could get flooded twice: once by Irene and once by a utility trying to save an overwhelmed dam.

New York lifted its evacuation order for 370,000 people and said subway service, shut down for the first time by a natural disaster, will be partially restored Monday, though it warned riders to expect long lines and long waits. Philadelphia restarted its trains and buses.

More On This...

    "All in all," New York Mayor Michael Bloomberg said, "we are in pretty good shape."

    The main New York power company, Consolidated Edison, didn't have to go through with a plan to cut electricity to lower Manhattan to protect its equipment. Engineers had worried that salty seawater would damage the wiring.

    Later in the day, the extent of the damage became clearer. Flood waters were rising across New Jersey, closing side streets and major highways including the New Jersey Turnpike and Interstate 295.

    In Essex County, authorities used a five-ton truck to ferry people away from their homes as the Passaic River neared its expected crest Sunday night.

    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 washed out 137 miles of the state's main highway.

    In Massachusetts, the National Guard had to help people evacuate. The ski resort town of Wilmington, Vt., was flooded, but nobody could get to it because both state roads leading there were underwater.

    "This is the worst I've ever seen in Vermont," said Mike O'Neil, the state emergency management director.

    Rivers roared in New Jersey and Pennsylvania. In the Hudson Valley town of New Paltz, N.Y., so many people were gathering to watch a rising river that authorities banned alcohol sales and ordered people inside. And in Rhode Island, which has a geography thick with bays, inlets and shoreline, authorities were worried about coastal flooding at evening high tide.

    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.

    The entire Northeast has been drenched this summer with what has seemed like relentless rain, saturating the ground and raising the risk of flooding, even after the storm passes altogether.

    The storm system knocked out power for 4 1/2 million people along the Eastern Seaboard. Power companies were picking through uprooted trees and reconnecting lines in the South and had restored electricity to hundreds of thousands of people by Sunday afternoon.

    Virginia Gov. Bob McDonnell had initially warned that Irene could be a "catastrophic" monster with record storm surges of up to 8 feet. But the mayor of Virginia Beach, Va., suggested on Twitter that the damage was not as bad as feared, as did the mayor of Ocean City, Md.

    One of two nuclear reactors at Calvert Cliffs, Md., automatically went offline because of high winds. Constellation Energy Nuclear Group said the plant was safe.

    The casinos of Atlantic City, N.J., planned to reopen Monday at noon after state officials checked the integrity of the games, made sure the surveillance cameras work, and brought cash back into the cages under state supervision. All 11 casinos shut down for the storm, only the third time that has happened.

    In Philadelphia, the mayor lifted the city's first state of emergency since 1986. The storm was blamed for the collapses of seven buildings, but no one was hurt and everyone was accounted for. People kept their eyes on the rivers. The Schuylkill was expected to reach 15 feet.

    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.

    As the East Coast cleans up, it can't afford to get too comfortable. Off the coast of Africa is a batch of clouds that computer models say will probably threaten the East Coast 10 days from now, weather officials said. The hurricane center gave it a 40 percent chance of becoming a named storm over the next two days.

    As the storm lost strength, more than 4.5 million East Coast homes and businesses lost power, and at least 21 deaths were blamed on the storm.

    "I think it's a little strong to say we dodged a bullet. However, it certainly could have turned out worse for the Hampton Roads area" in Virginia, said National Weather Service meteorologist Mike Montefusco.

    Officials warned that storm runoff was still making its way to rivers and creeks, leading to the possibility of extreme flooding. Irene was still packing winds of 50 mph extending for more than 300, but was expected to continue weakening as it moved through eastern Canada.

    Public transit in East Coast cities began to resume on Sunday, and New York said that its airports would reopen Monday morning. More than 11,000 flights were canceled because of the storm, and flight tracking services warned that hundreds more would be scrubbed on Monday. Trains and buses up and down the coast were also canceled.

    Irene menaced other cities as it roared northward, unloading a foot of rain on North Carolina and Virginia. As the eye of the sprawling storm blew through America's largest city and Long Island to the east, it pushed an 8-foot Atlantic storm surge toward New York and sent salty floodwater flowing into lower Manhattan.

    Federal Emergency Management Agency chief Craig Fugate said flooding, weakened trees and downed power lines are dangerous. He's advising people to stay inside, stay off the roads, and let power crews do their job.

    Briny water from New York Harbor submerged parts of a promenade at the base of the island. A foot of water rushed over the wall of a marina in front of the New York Mercantile Exchange, where gold and oil are traded.

    In the Broad Channel section of Queens, department rescue workers were riding in boats to search bungalows that were floating down the street to make sure no one was inside.

    Altogether, the FDNY has rescued 61 adults and three babies from 21 houses.

    In Times Square, shops boarded up windows and sandbags were stacked outside of stores. Construction at the World Trade Center site came to a standstill.

    New York has seen only a few hurricanes in the past 200 years. The Northeast is much more accustomed to snowstorms -- including a blizzard last December, when Mayor Michael Bloomberg was criticized for a slow city response.

    Authorities undertook the Herculean job of bringing the city to a halt Saturday when the subway system began shutting down at noon -- the first time the system was closed because of a natural disaster. Metro North commuter rail reported massive flooding along three lines.

    Tornadoes were reported in Maryland and Delaware, and several warnings were issued elsewhere, including New York and Philadelphia.

    Irene made landfall just after dawn Saturday near Cape Lookout, N.C., at the southern end of the Outer Banks. Shorefront hotels and houses were lashed with waves, two piers were destroyed and at least one hospital was forced to run on generator power.

    More than 1 million homes and businesses lost power in Virginia alone, where four people were killed by falling trees, at least one tornado touched down and about 100 roads were closed. Eastern North Carolina got up to 14 inches of rain, according to the National Weather Service. Virginia's Hampton Roads area was drenched with at least 9 inches, and up to 16 inches in some places.

    North Carolina Gov. Beverly Perdue said Irene inflicted significant coastal damage, but some areas were unreachable because of high water or downed power lines.

    A nuclear reactor at Maryland's Calvert Cliffs went offline automatically when winds knocked off a large piece of aluminum siding late Saturday night. Constellation Energy Nuclear Group spokesman Mark Sullivan said the facility and all employees were safe.

    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. Experts say Irene is threatening more people than any other hurricane in U.S. history.

    In Philadelphia, Mayor Michael Nutter declared a state of emergency, the first for the city since 1986, when racial tensions were running high. "We are trying to save lives and don't have time for silliness," he said.

    The storm hit Washington just days after an earthquake damaged some of the capital's most famous structures, including the Washington Monument.

    Pennsylvania Gov. Tom Corbett warned that the state will not necessarily be out of danger once the storm has passed.

    Irene caused flooding from North Carolina to Delaware, both from the 7-foot waves it pushed into the coast and from heavy rain.

    More than one million of the homes and businesses without power were in Virginia and North Carolina, which bore the brunt of Irene's initial fury. Irene caused flooding from North Carolina to Delaware, both from the 7-foot waves it pushed into the coast and from heavy rain.

    North Carolina Gov. Beverly Perdue said Irene inflicted significant coastal damage, but some areas were unreachable because of high water or downed power lines.

    A nuclear reactor at Maryland's Calvert Cliffs went offline automatically when winds knocked off a large piece of aluminum siding late Saturday night. Constellation Energy Nuclear Group said the facility and all employees were safe.

    In New Jersey, the Oyster Creek nuclear plant, just a few miles from the coast, shut down as a precaution as Irene closed in. And Boston's transit authority said all bus, subway and commuter rail service were suspended Sunday.

    "The rivers may not crest until Tuesday or Wednesday. This isn't just a 24-hour event," he said.

    Fox News has confirmed 24 deaths attributed to the storm included six in North Carolina, four in Virginia, four in Pennsylvania, two in New York, two in rough surf in Florida and one each in Connecticut, Maryland and New Jersey.

    The Associated Press contributed to this report.