"There were several serious injuries," said Cory Angell, spokesman for the Pennsylvania Emergency Management Agency. He said 73 people had been taken to 10 regional hospitals for treatment.
Among those in the pileup, but not seriously injured, was the Pennsylvania State University Lehigh Valley men's basketball team, which was on its way to a game in New Kensington, Pa., when its bus was hit by a tractor-trailer.
University officials were notified between 9:45 and 10 a.m., and the students were examined on the bus and transported to a shelter in Jonestown, said Penn State Lehigh Valley spokeswoman Kate Morgan.
The team returned home early Saturday afternoon and the athletes were examined "as a precaution" at Lehigh Valley-area hospitals, she said.
On its website, Penn State said that the team's chartered bus was struck by a tractor-trailer near Frystown, in Lebanon County. "As of 8 p.m. all 12 members of the basketball team as well as 3 coaches have been examined by hospital personnel," the university said. "None of their injuries were life-threatening and most have already been released to their families and are on their way home. One student awaits further testing."
Cars were smashed into one another at angles. Other vehicles careened into tractor-trailers, and at least one tractor-trailer was on its side.
In the accident area, I-78 was snow-covered, and there was snow on the grass and shoulder of the road.
"So happy me and my sister and her boyfriend are safe. This is insane," said one tweet from Caity Stout, who posted a photo of piled up cars. "We were in the middle of that bad pileup on I-78," she wrote.
"On the way to meet and get stopped 50 yards away from a 20 car pileup with 5 tipped over trucks," tweeted another person, Cooper Leslie, on Saturday morning.
More than 50 vehicles were involved, on both sides of I-78 at mile marker 7.5, said Trooper David LeBron of the Jonestown State Police Barracks.
"There were multiple injuries," LeBron said.
Thirteen patients were taken to Penn State Hershey Medical Center. Some arrived in helicopters, said Hershey spokeswoman Megan Manlove.
Three patients had critical injuries, requiring immediate medical attention. "I can't say whether they needed surgery," Manlove said.
Three suffered moderate to severe injuries, which could be something like a broken arm. "But I can't say specifically," Manlove said, noting that seven patients had minor injuries.
She said she wasn't aware that any of the accident victims brought to Hershey Medical Center were fatalities.
WellSpan Good Samaritan Hospital in Lebanon received six patients. They came by ambulance, and five of the six were "in good condition and expected to be treated and released," said hospital spokeswoman Cindy Stauffer.
The sixth was being transferred "for a higher level of care," she said.
People whose cars were involved in the huge pileup were kept warm in the back of tractor-trailers until rescue buses arrived, LeBron said. Area temperatures after the crashes were reported at 15 degrees, with light snow, according to the National Weather Service.
State police from Harrisburg also responded, LeBron said, as did several fire companies. LeBron said he had personally driven that stretch of highway earlier Saturday, and road conditions at the time were not slippery. "There was a snow squall that moved through, and visibility could have been a factor."
The Pennsylvania Emergency Management Agency sent a representative to the accident scene. The Lebanon County and Berks County Emergency Operations Centers were also involved, Angell said.
Red Cross workers assisted at the shelter set up at the Jonestown Fire Department. The state Departments of Military and Veteran Affairs, Human Services, and Health were on call to help at the shelter if needed, Angell said.
A special "state response team" went to nearby Fort Indiantown Gap to bring stockpiled food, water, and supplies to the shelter, if required, Angell said.
Staff writers Justine McDaniel and Bob Fernandez contributed to this article.