Lorries and other vehicles slammed into each other during a snow squall on an icy interstate motorway in Pennsylvania on Monday, creating a pile-up that killed at least three people and injured more than a dozen.
The crash on Interstate 81 was captured in videos posted on social media that show drivers and passengers lining the snowy road and jumping out of the way as a cascade of crashes unfolds in less than a minute.
Dr David Moylan, the Schuylkill County coroner, said three deaths had been confirmed by late afternoon and that number could rise because fires were impeding rescuers.
In one video, an out of control tractor-trailer smashes into a large dump lorry, turning it nearly 180 degrees.
Another catches fire and spews black smoke into the air, and an SUV hits a car, sending it spinning narrowly past a person standing on the shoulder in snow and fog.
The Schuylkill County Office of Emergency Management said the crash in north-east Pennsylvania happened about 10.30am on Monday.
John Blickley, the agency’s deputy co-ordinator, said officials believe a snow squall clouded visibility and probably contributed to the accident.
Estimates of the number of vehicles involved from the agency and state police ranged between 40 and 60, including tractor trailers.
Mr Blickley said emergency personnel from four different counties took about 20 patients to hospitals for treatment.
Three tractor trailers carrying unknown cargo were on fire when emergency personnel arrived and some smaller vehicles were also on fire ablaze he said.
Pennsylvania State Police Trooper David Beohm said on Monday afternoon that police hadn’t been able to investigate yet because a fire was still burning among some crashed cars and trucks.
Fire units on the scene included a steady stream of water tankers because “in the middle of nowhere, you have to bring your own water … there’s not a fire hydrant out here anywhere", Mr Beohm said
The motorway was covered in snow when the squall came through, he said.
“All it takes is one person to crash into something and you have to pull off the road, but when you continue to drive at highway speed, this is what happens,” he said.
The National Weather Service had warned of “numerous brief heavy snow squalls with very poor visibility".
“The squalls will quickly reduce the visibility to under one-half of a mile and coat the roads with snow,” forecasters said.
They urged drivers to get off the road if possible or turn on hazard lights, “and gradually slow down to avoid a chain reaction vehicular accident".
Mike Colbert, a forecaster with the weather bureau office in State College, said the weather service started issuing warnings for snow squalls a few years ago, and pile-ups of the kind being reported were the reason they began doing so.
“They are very heavy snow showers where if you are driving into them, you can go from partly cloudy or sunny skies into an instant blizzard in a matter of seconds. That’s why they are so dangerous,” Mr Colbert said.