In Boston, temperatures were set to beat that at minus 20 degrees, even lower in mountainous areas, the National Meteorological Service warned, announcing an alert for the states of New York, New Jersey, Maine and Connecticut.

"The first shot of Arctic wind which arrived Tuesday evening has already produced wind chill values as low as 10 degrees below zero across the (New York) metropolitan area during the morning hours," the NMS said Wednesday.

"As weak high pressure builds over the area this afternoon, winds will diminish and wind chill values will rise to above zero.

But with "a new round of reinforcing Arctic air" to pour into the region Thursday night, the weather service warned that wind chill would approach "dangerous levels of 20 to 25 below zero."

The effect is due to air temperatures falling to between zero and five degrees combined with northwesterly winds of 32-40 kilometers (20-25 miles) an hour, the service said, warning that exposed skin at such readings "can become frostbitten in 30 minutes."

In some part of the US North-East, snow could fall to a depth of 10 centimeters (four inches), it added.

In southeast Canada Wednesday the wind chill factor forced temperatures down to minus 40 degrees.

TERRA.WIRE