NEW YORK - One month into one of the mildest winters on record in the Northeast, an arctic blast sent temperatures into the danger zone Friday, and New York gave its police legal authority to remove homeless people from the streets to keep them from freezing to death.

Temperatures from Maine to Pennsylvania were in the single digits and the teens, with lows of minus-10 recorded in northern Pennsylvania.

The temperature in Central Park was 9 degrees before daybreak and reached 12 degrees by dawn, but the wind chill made it feel like minus 6.

City officials declared a weather alert that gave police power to remove hundreds of homeless people from the streets and put them in shelters. Authorities are normally not permitted to force anyone off the street without their consent.

"Though we haven't had much snow, winter has finally showed its nasty bite," said the Web site of the New York City Rescue Mission in Manhattan.

By midday, the city received nearly 2,000 calls from people complaining they had no heat or hot water.

In Pennsylvania, schools delayed openings so students would not have to wait for their school buses in the early morning cold.

Forecasters attributed the extreme cold to a southern shift in the jet stream. The high-altitude air current has been running much farther north than usual over the East Coast, allowing warm air to invade from the South.