A total of five people have now been pronounced dead, WFMZ-TV reports.
Dozens of others were injured when tractor-trailers and other vehicles lost control and slammed into each other during a snow squall.
Interstate 81 north in Schuylkill County remained closed Tuesday morning following the wreck amid poor visibility that involved between 40 and 60 vehicles, authorities and published reports say.
Numerous vehicles remained on the roadway in the northbound lanes early Tuesday, authorities said.
Some vehicles were mostly burned and others melted onto the highway, and authorities said they needed to go through each vehicle to make sure there are no human remains.
After the larger vehicles are removed and the road is cleared of debris, Pennsylvania Department of Transportation crews will need to remove a layer of the road surface due to spilled liquids such as fuel and oil from the crashed vehicles, PennDOT spokesperson Ronald Young said Tuesday afternoon. The roadway could be open by Wednesday morning.
The crash Monday on Interstate 81 was captured in videos posted on social media that showed drivers and passengers lining the snowy road and jumping out of the way as the cascade of crashes unfolded.
In one video, an out of control tractor-trailer smashed into a large dump truck turning it nearly 180 degrees, another large truck caught fire and spewed black smoke into the air, and an SUV struck a passenger car sending it spinning narrowly past a person standing on the shoulder in snow and fog.
The north and southbound lanes of the highway were closed for several hours after the accident, but the southbound side reopened around 6:30 p.m. Monday.
WFMZ-TV and the Associated Press contributed to this report.