A dangerous cold snap bringing life-threatening cold was settling in across the northeastern US on Saturday and a snow squall triggered a pileup of dozens of vehicles on a Pennsylvania highway that left several people dead.

Officials warned people to stay indoors away from what the National Weather Service described as "life threatening" cold. Wind chill advisories were in effect over parts of nine states extending from northern Pennsylvania to western Maine, with forecasters expecting gusts up to 45 miles per hour (72 kph).

While the storm was not bringing much snow to region, a squall outside Harrisburg, Pennsylvania triggered a pileup of more than 50 cars and trucks, shutting an interstate highway, state police said. Multiple people died in the accident, the Pennsylvania Emergency Management Agency said on its web site.

The agency did not say how many people had died and a spokesperson could not be reached for immediate comment.

Officials warned that the cold would intensify through the day and into Sunday.

"Wind chills will be getting colder and colder as the day goes on," said Alan Dunham, a meteorologist with the National Weather Service in Taunton, Massachusetts.

The temperature in Boston was expected to drop to -7 degrees Fahrenheit overnight (-21.7°C), but feel as cold as -30 degrees Fahrenheit (-34.4°C) with the wind chill.

New York City was bracing for its coldest night in 20 years. Mayor Bill de Blasio said officials had put on extra staff to help residents who had lost heat.

"It's so important to take this seriously, to stay indoors to the maximum extent possible," de Blasio told reporters.

At Boston's Pine Street Inn 485-bed homeless shelter, workers were finding cots, mats and even chairs to accommodate the roughly 600 people they were expecting tonight, said spokeswoman Barbara Trevisan.

"No one will be turned out for lack of space," Trevisan said.

In Boston, some hurried through their mornings to get outdoor chores done before the worst cold set in.

"Right now I'm going to drink a coffee" to stay warm, said Carmen Pichente, 40, en route to her job at a Boston restaurant. "Tomorrow, I'm going to stay at home all day."

Others brushed it off.

"It's nothing. I lived in Boston all my life," said Eddie Brown, 51, a delivery truck driver out on his rounds. Asked why he wasn't wearing a coat, Brown replied, "I got long underwear on." – Reuters