People wait at a bus stop during a snow storm in New York's financial district on Wednesday.

New York - A wintry storm dropped snow on the US Northeast on Wednesday and threatened to bring dangerous winds and flooding to a region still climbing out from the devastation of superstorm Sandy.

The nor'easter storm added misery to thousands of people whose homes were destroyed by Sandy, which killed 120 people when it smashed ashore on October 29 in the New York-New Jersey area, swallowing entire neighbourhoods with rising seawater and blowing homes from their foundations.

Some 650 000 homes and businesses still lacked power in the region from one of the biggest and costliest storms ever to hit the United States.

Airlines cancelled more than 1 200 flights, tracking service reported.

New York and New Jersey evacuated the most vulnerable areas ahead of the nor'easter, whose rain, strong winds and snow were expected to hit a large portion of the Northeast region.

The low-pressure system was forecast to strengthen as it moved north on Wednesday with wind gusts up to 96km/h, the National Weather Service said.

Ice pellets hit Long Island and the storm lifted wave heights to nearly six metres off Nantucket, Massachusetts, AccuWeather reported.

School districts in Connecticut sent students home early as a precaution, and the New York Stock Exchange removed the giant US flag from its facade to protect it from high winds.

Snowflakes or a mix of rain and snow fell on parts of New York, New Jersey, Connecticut and Pennsylvania, causing airport delays.

American Airlines suspended operations in Philadelphia and at the major New York-area airports on Wednesday, but said it expected them to resume on Thursday. The AMR Corp unit said 365 flights were cancelled for Wednesday and Thursday.

United Continental cancelled about 500 flights for Wednesday and Thursday because of the storm. That figure accounted for less than five percent of its total flights scheduled for the time period. Delta Air Lines said it had about 150 cancellations at the three major New York airports and Philadelphia.

Just across the New York City line in the Long Island community of Cedarhurst, the curb was piled high with damaged wood doors, bookshelves, oil burners, couches and rugs from Sandy - debris that people feared could become deadly projectiles in the wind.

Water had rushed through Cedarhurst like a river during the Sandy, forcing Rudi Schlachter, 34, to move her family to the upper floors of their house.

“All you need is a gale of wind driving a piece of wood into somebody's window,” Schlachter said in front of her home, which had just regained electricity but still lacked heat because of Sandy. “We're leaving. I don't want my kids to see the water again.”

Many gasoline stations remained shut in Cedarhurst, complicating efforts for people to flee the new storm.

Of five gas stations along a stretch of road near Cedarhurst just south of John F. Kennedy International Airport, none had gas Tuesday night and one, a Shell station, received a delivery on Wednesday morning. The lines there were more than two hours long.

“There's fights over and over and people are cursing,” said Gege Chawla, an occupational therapist whose father owns the Shell station.

New York Mayor Michael Bloomberg closed parks and beaches and temporarily halted outdoor construction ahead of the storm.

On the devastated New Jersey shore, a summer tourist haven where Sandy's storm surge pushed entire homes across the street, the town of Brick issued a mandatory evacuation order for waterfront neighbourhoods ahead of Wednesday's storm. Middletown also ordered evacuations.

The Federal Emergency Management Agency said it was working with state and local authorities and was “ready to deploy additional resources if needed to respond to the nor'easter”.

President Barack Obama won wide praise for the US government's response to Sandy, which may have helped him win re-election on Tuesday against Republican challenger Mitt Romney.

Bloomberg endorsed Obama for a second term after Sandy struck, citing his record on climate change. Regardless of whether climate change was to blame for a rise in severe weather events, it should compel leaders to act on the issue, the mayor said.

Sandy struck one week before the US elections, prompting New Jersey to take the uncommon step of allowing storm-displaced voters to cast ballots by email or fax, while New Yorkers were able to vote at any polling place by presenting an affidavit.

Makeshift polling places were also set up, but some voters still faced chaotic scenes and long lines. - Reuters