Transportation officials warned of extensive delays and street closures and urged drivers to avoid the area in the northeast corner of the city. Officials said the tanker may have been hauling hundreds of gallons of gasoline. 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. There were no reports of injuries.

The northbound lanes of I-95 were gone, and the southbound lanes were “compromised” due to heat from the fire, said Derek Bowmer, battalion chief of the Philadelphia Fire Department. Runoff from the fire or perhaps broken gas lines were causing explosions underground, he added.

Some kind of crash happened on a ramp underneath northbound I-95 around 6:15 a.m. The northbound section above the fire collapsed quickly, state Transportation Department spokesman Brad Rudolph said.

Mark Fusetti, a retired Philadelphia police sergeant, said he was driving south toward the city’s airport when he noticed thick 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.”

The southbound lanes were heavily damaged, “and we are assessing that now,” Rudolph said Sunday afternoon.

There was no immediate time frame for reopening the highway, but Rudolph said officials would consider “a fill-in situation or a temporary structure” to accelerate the effort.

Motorists were sent on a 43-mile (69-kilometer) detour, which was going “better than it would do on a weekday,” Rudolph said. The fact that the collapse happened on a Sunday helped ease congestion.

He expected traffic “to back up significantly on all the detour areas.”

Most drivers traveling the I-95 corridor between Delaware and New York City use the New Jersey Turnpike rather than the segment of interstate where the collapse occurred. Until 2018, drivers did not have a direct highway connection between I-95 in Pennsylvania and I-95 in New Jersey. They had to use a few miles of surface roads, with traffic lights, to get from one to the other.

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.

Thousands of tons of steel and concrete were piled atop the site of the fire, he said, and heavy construction equipment would be required to start to remove the debris.

The fire was strikingly similar to another blaze in Philadelphia in March 1996, when an illegal tire dump under I-95 caught fire, melting guard rails and buckling the pavement.

The highway was closed for several weeks, and partial closures lasted for six months. Seven teenagers were charged with arson. The dump’s owner was sentenced to seven to 14 years in prison and ordered to pay $3 million of the $6.5 million repair costs, The Philadelphia Inquirer reported.

More recently in Atlanta, an elevated portion of Interstate 85 collapsed in a fire, shutting down the heavily traveled route through the heart of the city in March 2017. A homeless man was accused of starting the blaze, but federal investigators said in a report that the state transportation department’s practice of storing combustible construction materials under the highway increased the risk of fire.

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Associated Press writers Mark Scolforo in Harrisburg, Pennsylvania, and Jake Offenhartz in New York contributed to this report.