An overpass on one of America's busiest highways collapsed early Sunday after a tanker crossing underneath burst into flames, Pennsylvania's governor said, predicting it will take months to fully restore the "critical artery."

Governor Josh Shapiro said at an afternoon press briefing that surprisingly no one traveling along Interstate 95 above the blaze had been injured, but that authorities were working to "identify any individual or individuals who may have been caught in the fire" below.

With roughly 160,000 vehicles per day passing through that section of highway in northeastern Philadelphia, according to the state's transportation secretary, the collapse is likely to lead to major traffic delays just as the summer holiday season gets underway.

Interstate 95 (I-95) connects major cities along the US East Coast from Maine to southern Florida.

Shapiro said that the northbound side of the road had completely collapsed in the fire, while the southbound lanes had been deemed structurally unsound. A "complete rebuild" is expected to take a "number of months," he said.

"This is a major artery for people and goods, and the closure will have significant impacts on the city and region," US Secretary of Transportation Pete Buttigieg said on Twitter, adding that his office will "be there with support throughout the process of I-95 returning to normal."

Shapiro said he will sign a disaster declaration on Monday to help free up funds for the repairs.

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.

- 'Remarkable devastation' -


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.

Shapiro told the press conference he had taken an aerial survey of the damage, describing it as "remarkable devastation."

"I found myself thanking the Lord that no motorists who were on I-95 were injured or died," he said.

The fire started around 6:20 am (1020 GMT), he said, when Sunday traffic is typically light, though videos showed drivers on the highway trying to navigate the unfolding disaster in real time.

Residents told local media outlets that they heard several explosions, which Battalion Chief Derek Bowmer of the Philadelphia Fire Department said earlier in the day were coming from underground, caused by runoff from the truck.

Authorities said they were rushing to increase capacity on public transit in the area to help commuters, and evaluating different options for longer-term detours around the collapsed section.

That portion of I-95 runs nearby the Delaware River, but local officials said the wreckage did not pose any environmental threats to the water.

"I hope it's clear to everyone to here that every agency -- local, state and federal -- are working together to address this," said Shapiro.