The driver of a petrol tanker lost control on an off-ramp and flipped the lorry on its side, resulting in a fiery wreck that destroyed a section of the East Coast’s main north-south motorway, Pennsylvania's top transport official said on Monday.
In the first official account of the accident that threw hundreds of thousands of morning commutes into chaos and disrupted untold numbers of businesses, state Transport Secretary Mike Carroll said the lorry was going northbound on Sunday when the driver lost control.
As a result, Interstate 95 will be closed in both directions for weeks right at the start of summer travel season.
The elevated southbound portion of I-95 will have to be demolished, as well as the northbound side, Mr Carroll said.
Motorists should avoid Pennsylvania's north-east corner, transport officials said.
As excavation teams laboured to clear rubble from the site on Monday, a body was recovered from the wreckage and turned over to the Philadelphia County Medical Examiner for identification, state police said in a statement.
The lorry driver, Nathaniel Moody, had been unaccounted for in the immediate aftermath of the accident, local ABC affiliate WPVI-TV reported.
Video from the scene showed a massive concrete slab had fallen from the I-95 on to the road below in north-east Philadelphia.
Derek Bowmer of the Philadelphia Fire Department said the northbound lanes of the I-95 were gone and the southbound lanes were “compromised” due to heat from the fire. He also said run-off from the fire or perhaps compromised gas lines were causing explosions underground.
US Transport Secretary Pete Buttigieg said the federal government was working with the state of Pennsylvania to restore the motorway.
“This is going to be a major disruption in that region,” Mr Buttigieg said. He did not specify a precise timetable for a fix but said “definitely not days. I mean, if it is weeks, we're not talking about a couple”.
The chief of the Federal Highway Administration plans to visit the site, White House spokeswoman Karine Jean-Pierre said. The US National Transportation Safety Board is investigating.
Officials were also concerned about the environmental effects of run-off into the nearby Delaware River.
The emergency management office said other streets had been closed and urged people to avoid the area. Officials planned to launch a drone to assess the damage.