A fire caused part of a busy US highway overpass to collapse in Philadelphia early Sunday, authorities said, as reports attributed the accident to an oil tanker that burst into flames under the bridge.

The collapse took out four traffic lanes along an elevated section of the heavily traveled motorway, though no injuries were immediately reported.

Images broadcast on television showed flames and billowing smoke coming from the crumbled section of Interstate 95 in the northeastern city's Tacony neighborhood, with parts of the elevated roadway having fallen onto the lanes below.

A city spokeswoman told AFP that a "large fire under I-95" caused the highway to collapse, but did not attribute it to any vehicle. She said the fire has been declared "under control."

Local media reported the fire started around 7:00 am when Sunday traffic is typically light.

The north-south highway -- one of the busiest in the United States, connecting Maine to Florida and major cities along the East Coast -- remained closed in both directions in the Philadelphia area, officials said.

"I-95 will be impacted for a long time, for a long time," Philadelphia Managing Director Tumar Alexander told a news conference, according to The Philadelphia Inquirer.

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.