Updated at 7.45am

A powerful storm is beginning to lash the north-eastern US prompting flight cancellations, school closures and warnings to stay off the roads.

The National Weather Service issued blizzard warnings for parts of Pennsylvania, New Jersey, New York, Connecticut, Rhode Island, Massachusetts, New Hampshire and Maine.

The storm was expected to dump up to two feet of snow on the New York City metro area with wind gusts of up to 55mph.

The weather service's office near Philadelphia called the storm "life-threatening" and warned people to "shelter in place". Coastal flood warnings were in effect from Massachusetts to Delaware.

According to the airline-tracking website FlightAware, more than 5,000 flights were cancelled on Tuesday, while the railways were also affected, and in New York City the above-ground parts of the subway system were being shut down.

In Massachusetts, where there were forecasts of 12 to 18 inches of snow, Governor Charlie Baker encouraged motorists to stay off the roads and to take public transport only if absolutely necessary.

The fast snowfall rates will "create hazardous driving conditions across the Commonwealth," he said.

Schools in New York City, Philadelphia, Boston and elsewhere were all closed on Tuesday.

In Maryland, Governor Larry Hogan declared a state of emergency and urged residents not to be lulled into a false sense of security due to the mild winter.

"This is a serious winter storm," he said, adding that some parts of the state could see 12 to 18 inches of snow.

"It's obviously going to be the biggest event we've had this season and people need to be prepared. They need to be safe."

Governor Tom Wolf of Pennsylvania said around 700 National Guard members would be deployed, along with more than 2,000 snow ploughs to cope with the storm that was expected to bring a foot or more of snow to some parts of the state.

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