An overpass on one of America's busiest highways collapsed early Sunday, caused by a tanker truck bursting into flames underneath it, authorities said.
The collapse took out four traffic lanes along an elevated section of the heavily travelled Interstate 95, though no injuries were immediately reported.
"Companies arrived on location and they found... heavy fire," battalion chief Derek Bowmer of the Philadelphia Fire Department told reporters Sunday morning.
US Transportation Secretary Pete Buttigieg said the vehicle on fire under the bridge was a tanker truck, after the fire department had already declared the situation a hazmat incident earlier in the day amid reports it might have been a tanker.
The north-south highway – one of the busiest in the US, connecting major cities along the East Coast from Maine to Florida – remains closed in both directions in the Philadelphia area, officials said.
Rebuilding the section of destroyed highway could take weeks, authorities said, a nightmare scenario for commuters as well as for road travellers at the start of the summer holiday season.
"This is a major artery for people and goods, and the closure will have significant impacts on the city and region," Buttigieg said on Twitter, adding that his office is offering "any assistance that (the US Department of Transportation) can provide to help with recovery and reconstruction."
"We expect significant regional traffic impact," he added.
Local media reported that Philadelphia police as well as the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) were looking for the driver of the vehicle associated with the fire, whose whereabouts are unknown.
An ATF spokesman told AFP that its Philadelphia field division "is supporting the investigation" and referred additional inquiries to the fire department. The fire department declined to comment.
'Heat and heavy fire'
The White House said President Joe Biden had been briefed on the situation and been in touch with local authorities to offer assistance.
Television images showed flames and billowing smoke coming from the crumbled section of I-95 in the northeastern city's Tacony neighborhood, with parts of the elevated roadway having fallen onto the lanes below.
Local media reported the fire started around 6.20am (0220 GMT), when Sunday traffic is typically light, though videos showed drivers on the highway trying to navigate the unfolding disaster in real time.
"I will always be grateful to our first responders for the dangerous, life-saving work they do to keep residents and visitors safe," Philadelphia Mayor Jim Kenney said on Twitter.
The southbound lanes of the highway, while still standing, are "compromised," Bowmer said. "They got a lot of heat and heavy fire."
"I-95 will be impacted for a long time, for a long time," city managing director Tumar Alexander told a news conference, according to The Philadelphia Inquirer.
Residents told local media outlets that they heard several explosions, which Bowmer said were coming from underground, caused by runoff from the truck.