Normally-bustling areas of New York City were nearly deserted and many businesses in the core were boarded up as the city braced for the arrival of Hurricane Irene Saturday night.

As coastal water levels began to rise in Manhattan and other areas, the city's mass transit had halted and the city had an eerie calm, following mandatory evacuations for 370,000 residents in low-lying areas.

The key concern for many local officials is that during high tide, at 8 a.m. Sunday, the storm could drive water over the shore and into the city.

CTV's Todd Battis reported from New York that locals were taking the evacuations and storm warnings seriously.

"We're heading through Times Square, and there's no traffic," he said, adding that the city seems nearly completely shut down.

"The tourists are hunkered down in their hotels and the locals have left."

The storm's death toll in the U.S. has reached six, and the brunt impact of the storm is expected in many cities late on Saturday and on Sunday morning.

By Saturday night, the storm was lashing the Hampton Roads region in Virginia and parts of Delaware and was still hundreds of kilometres from New York City.

Other cities along the Atlantic coast, like Washington, Boston and Philadelphia, were also bracing for the worst as Irene made landfall along the southern coast of North Carolina Saturday morning.

Though Irene has been downgraded to a Category 1 hurricane, the slow-moving storm is still packing intense, 130-kilometre-an-hour winds and heavy rain as it crawls up the East Coast.

But since the storm is only moving at 13 kilometres per hour, forecasters believe that heavy rains combined with high tides could cause serious flooding in many areas.

Evacuations have been ordered for about 2.3 million people in the heavily-populated hurricane path, which stretches from the Carolinas right up to Canada.

In Nova Scotia, Environment Canada issued a tropical storm warning on the province's south coast.

The U.S. National Hurricane Centre said that the centre of the storm, estimated to be about 1000 kilometres wide, was expected to lurch toward the mid-Atlantic coast on Saturday night.

"Irene is forecast to remain at or near hurricane strength as it moves near or over the mid-Atlantic states and approaches New England," the NHC reported.

Officials were also warning about a storm surge that could raise water levels by up to 2.5 metres along the coast, along with "destructive and life-threatening waves."

Rainfall accumulations of up to 60 centimetres have also been forecast in some areas and four deaths have been blamed on the storm.

Further north, New York City Mayor Michael Bloomberg appealed to residents to evacuate as soon as possible. By evening, water levels near Battery Park had already risen by about a foot (about 30 centimetres), CNN reported.

"The time to leave is right now," Bloomberg said at a press conference on Saturday morning. "Staying behind is dangerous, it's foolish and it's against the law."

He said it's conceivable that downtown Manhattan will have no electricity and a lot of water on the streets. He also urged business owners in the evacuation zones to close up shops and leave.

Many building managers have turned off elevators and warned occupants to stay away from windows, especially if they live above the tenth floor.

Officials are also concerned about storm surges that could swamp streets, subways and underground parking garages.

In evacuation areas, some landlords were estimating that between 50 and 80 per cent of apartment buildings were clear.

Transportation shutdowns: buses, subways and planes

Evacuation orders for the country's eastern seaboard covered at least 2.3 million people, including 1 million in New Jersey, 315,000 in Maryland, 300,000 in North Carolina, 200,000 in Virginia and 100,000 in Delaware.

"This is probably the largest number of people that have been threatened by a single hurricane in the United States," said Jay Baker, a geography professor at Florida State University.

The massive storm has also forced the country's biggest transit system to close. The city's public transportation system closed at noon on Saturday – the first shutdown brought on by a natural disaster. On an average weekday, the system carries about five million commuters.

Meanwhile, U.S. airlines cancelled thousands of flights through Monday, grounding hundreds of thousands of passengers as the storm could strike major airports from Washington to Boston.

With files from The Associated Press