Thousands of people have been ordered to evacuate coastal communities in the Northeast United States ahead of a superstorm that threatens to unleash high winds, heavy rains and mass flooding on the region.

New York Mayor Michael Bloomberg issued evacuation orders for lower Manhattan and other low-lying areas on Sunday, while tens of thousands of residents along the coastlines of Delaware, New Jersey and Connecticut have also been told to leave.

Officials announced that schools will remain closed in cities such as New York, Philadelphia, Washington, Baltimore and Boston. Public transit will shut down Sunday evening in New York and Philadelphia over flooding fears.

The storm, which is expected to make landfall late Monday night or early Tuesday, could dump as much as 30 centimetres of rain in some areas. Winds of 130 kilometres per hour may whip up waves as high as 3.3 metres. Some areas may receive as much as 60 cm of snow.

The storm will most likely make landfall in New Jersey. However, it is expected to impact a region spanning 1,300 km.

Officials in New York fear that high waves will send water rushing into not only the subway system, but the underground communications network that powers Wall St.

鈥淚f you don't evacuate, you are not only endangering your life, you are also endangering the lives of the first responders who are going in to rescue you," Bloomberg told residents of lower Manhattan and Queens.

"This is a serious and dangerous storm."

The city also postponed the reopening of the Statue of Liberty after a year-long, $30 million renovation.

There were at least 6,800 airline flight cancellations announced Sunday, something that is bound to impact travel and business across North America and over to Europe.

Emergency officials warned residents against underestimating the storm鈥檚 potential impact.

"The time for preparing and talking is about over," Federal Emergency Management Administrator (FEMA) Craig Fugate said. 鈥淧eople need to be acting now.鈥�

The storm will be the by-product of a collision between Hurricane Sandy, which devastated parts of the Caribbean late last week and is now churning up the Atlantic Coast, and two other weather systems: a winter storm coming in from the west and cold Arctic air.

The death toll from Sandy now stands at 65. Most of the victims were in Haiti.

U.S. President Barack Obama paused his campaign Sunday to meet with FEMA officials, and then to warn residents living in the storm鈥檚 path.

鈥淭his is a serious and big storm,鈥� he said. 鈥淎nd my first message to all the people across the Eastern seaboard, mid-Atlantic going north is that you need to take this very seriously.鈥�

Obama promised that federal agencies will 鈥渞espond big and respond fast鈥� after the storm.

The U.S. National Hurricane Center in Miami put Sandy about 780 kilometres southeast of New York City late Sunday evening. Sandy remained a Category 1 hurricane Sunday with winds of 120 kph.

Among the preparations for the superstorm鈥檚 arrival:

  • Amtrak cancelled some train service over the weekend, with plans to cancel nearly all trains in the Northeast by Monday evening.
  • Extra flights were added to Sunday schedules out of New York and Washington, ahead of expected mass cancellations.
  • In Virginia, 500 National Guard troops were called up to be ready for clean-up duty after the storm passes.
  • New Jersey Gov. Chris Christie declared a state of emergency, which closed Atlantic City casinos for only the fourth time in 34 years.
  • In New York, Broadway performances for Sunday and Monday evening were cancelled, while the New York Stock Exchange planned to keep its trading floor closed, but allow for electronic trading.

Wilmington, Del. resident Bobbie Foote said she would obey a local evacuation order and take shelter at her daughter鈥檚 home in Newark.

Foote, 58, remained in her home last year when Hurricane Irene hit, which left several streets in her neighbourhood blocked.

鈥�(My daughter) said I should never put myself in that predicament where I cannot get in or out of where I live," Foote said.

With a report from CTV鈥檚 Joy Malbon and files from The Associated Press