PHILADELPHIA (AP) — An elevated section of Interstate 95 collapsed early Sunday in Philadelphia after a vehicle caught fire, closing the main north-south highway on the East Coast and threatening to upend travel in parts of the densely populated Northeast, authorities said.

Early reports indicated that the vehicle may have been a tanker truck, but officials could not immediately confirm that. The fire was reported to be under control.

Video from the scene showed a massive concrete slab had fallen from I-95 onto the road below in northeast Philadelphia. There were no immediate reports of injuries.

Capt. Derek Bowmer of the Philadelphia Fire Department said the northbound lanes of I-95 were gone and the southbound lanes were “compromised” due to heat from the fire. He also said runoff from the fire or perhaps compromised gas lines were causing explosions underground.

Mark Fusetti, a retired Philadelphia police sergeant, said he was driving south toward the city’s airport when he noticed thick plumes of black smoke rising over the highway. As he passed the fire, the road beneath began to “dip,” creating a noticeable depression that was visible in video he took of the scene, he said.

He saw traffic in his rearview mirror come to a halt. Soon after, the northbound lanes of the highway crumbled.

“It was crazy timing,” Fusetti said. “For it to buckle and collapse that quickly, it’s pretty remarkable.”

Officials were also concerned about the environmental effects of runoff into the nearby Delaware River.

“Today’s going to be a long day. And obviously, with 95 northbound gone and southbound questionable, it’s going to be even longer than that,” said Dominick Mireles, director of Philadelphia’s Office of Emergency Management.

Heavy construction equipment would be required to start to remove the debris, he said.

The emergency management office said other streets were closed and urged people to avoid the area. Officials planned to launch a drone to assess the damage.