A general view shows the partial collapse of Interstate 95 after a fire underneath an overpass in Philadelphia on Sunday. Reuters

A fire caused an overpass on one of America's busiest highways to collapse on Sunday in Philadelphia, authorities said, as reports attributed the cause to a truck that burst into flames under the bridge.

The collapse took out four traffic lanes along an elevated section of heavily travelled Interstate 95, though no injuries were immediately reported.

"Companies arrived on location and they found... heavy fire from a vehicle -- we don't know what type of vehicle it was," Captain Derrick Bowmer, of the Philadelphia Fire Department, told a news conference.

Bowmer added the situation was considered a hazmat incident, but could not confirm reports that the burning vehicle was an oil tanker.

Federal and local law enforcement are looking for the driver, whose whereabouts are unknown, local media reported.

The north-south highway -- one of the busiest in the United States, 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 travelers at the start of the summer holiday season.

"Avoid area. Plan and seek alternative travel routes," the Philadelphia Office of Emergency Management said in a tweet.

US Secretary of Transportation Pete Buttigieg said on Twitter he is offering "any assistance that USDOT can provide to help with recovery and reconstruction."

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.

City authorities issued a series of alerts on Twitter about a tanker truck fire on the highway, which local media reported caught fire underneath the bridge, apparently causing the collapse.

Agence France-Presse