NEW YORK (AFP) - A fierce winter storm brought chaos to the northern United States (US) on Friday, killing at least 11 people and forcing the cancelation of thousands of flights.

More than 61cm of snow fell in parts of Massachusetts town as a state of emergency was declared in New York and New Jersey states.

One worker was killed when a 31m pile of salt being prepared to treat roads in the Philadelphia region fell on him, media reports said.

A 71-year-old woman suffering from Alzheimers disease froze to death after walking out into the cold and getting lost in northern New York state, authorities said.

At least nine other deaths were blamed on the storm - named Hercules - that caused traffic accidents and other disruption across 22 states and parts of Canada.

Hercules closed major roads for several hours with snowdrifts built up by Arctic winds of up to 105kmh.

Weather experts said the windchill temperature would plummet to -25 degrees Celsius in New York state.

More than 4,200 international and domestic flights were cancelled at airports along the east coat and as far as Chicago on Thursday night and Friday. Thousands more were delayed.

New York's John F. Kennedy Airport closed for several hours because of poor visibility and high winds.

Flights were also cancelled at Chicago, Boston, Philadelphia and other key airports.

Boston woke up to a temperature of about -16 degrees Celsius but with the wind chill, it felt much worse.

Essex county in Massachusetts recorded 61cm of snow.

Much of the state's Atlantic coastline was put on flood alert.

The New York and New Jersey governors ordered major roads closed during the worst of the blizzard, but they were reopened on Friday morning.

Government leaders still appealed for people to stay home unless they had urgent business.

The storm was the first big test for New York City's new Mayor Bill de Blasio, who only took up his job on Wednesday.

Mr De Blasio had vowed a "laser focus" on the storm. But the mayor also urged residents to stay indoors and warned against going out in the freezing temperatures.

Mr De Blasio shovelled snow from in front of his Brooklyn house on Friday before repeating appeals for drivers to stay off the streets to help the city clear its 9,900km of roads.

"If you want safe, clear streets, stay home," he said.

Tourists lobbed snowballs at each other in Times Square and more than 15cm of snow fell on Central Park.

But 450 salt spreaders were out across the city and 1,700 refuse trucks had been fitted with plows in a bid to keep New York moving. The city set up a special website and app, PlowNYC, so residents could follow street clearances in real time.

Many metro trains were cancelled or delayed however and schools and many businesses remained closed in all the affected states.

And sub-freezing temperatures are expected as far south as Florida, the National Weather Service said.

Officials backed Mr de Blasio's warning about going out in the cold as night fell again and temperatures plummeted.

Experts said that winds of 48kph could cause frostbite in about 30 minutes.