PHILADELPHIA -- A winter storm that brought snow and ice to the U.S. East Coast moved off-shore Friday, leaving at least 25 people dead and hundreds of thousands without power and causing a large pileup in Pennsylvania that injured 30 people.

The deaths included a pregnant woman struck by a mini-plow in New York City whose baby was then born by cesarean section and two people killed when they tried to aid a truck driver on a snow-covered interstate in North Carolina.

Across the U.S., this is shaping up as one of the snowiest winters on record. As of early this month, Washington, Detroit, Boston, Chicago, New York and St. Louis had gotten roughly two or three times as much snow as they normally receive at this point in the season.

The latest go-round of bad weather came just in time to delay tens of thousands of deliveries of Valentine's Day flowers, dropping snow, sleet and rain on roads already covered with deep puddles and icy patches.

The snow, sleet and ice that bombarded the Southeast on Wednesday brought its ferocity into the Northeast on Thursday and Friday.

Numerous traffic accidents involving multiple tractor-trailers and dozens of cars completely blocked one side of the Pennsylvania Turnpike outside Philadelphia on Friday morning and injured 30 people, none seriously. The crashes were reported about five hours after snow ended. Speed restrictions enacted during the storm had been lifted, but motorists say the roadway was coated with ice.

By the time it stopped falling, 22.5 inches (57 centimetres) of snow was reported in one Pennsylvania County. Parts of upstate New York got up to 27 inches (68.5 centimetres). Washington, D.C., received 9 inches (23 centimetres) of snow Thursday, while New York City got nearly 10 inches (25 centimetres).

The sloppy mix of snow and face-stinging sleet grounded more than 6,500 flights nationwide on Thursday and about 2,100 more on Friday. About 1.2 million utility customers lost power as the storm moved from the South through the Northeast, dropping to about 450,000 outages by Friday morning, mostly in South Carolina and Georgia.

Many schools remained closed Friday in eight states from Virginia to Maine.

The treacherous weather was blamed for more than two dozen deaths, many of them in motor vehicle accidents.

In North Carolina, two Good Samaritans were killed Thursday night when they tried to help the driver of tractor-trailer cab that spun out on a snow-covered highway. Another driver faces second-degree murder and other charges in the hit-and-run wreck, the state Highway Patrol said.

In New York, 36-year-old Min Lin died after she was struck by a utility vehicle with a snowplow attached to it as it backed up outside a shopping centre in Brooklyn. She was rushed by paramedics to a medical centre, where her nearly full term, baby was delivered via cesarean section.

The baby remained in critical condition Friday evening, according to a spokeswoman for Maimonides Medical Center.

The driver, 42-year-old Wu Wu, was issued summonses Friday for not having the vehicle inspected and not having a headlamp or a license plate light. No criminal charges have been filed.