Pittsburgh police have reopened Grant Street to one lane after it was closed to traffic in Downtown Pittsburgh as two manhole covers along the thoroughfare popped loose, one with a thunderous boom, around noon Tuesday.

The cause was traced to a fire affecting electrical wires under Grant Street, according to Emily Bourne, a police spokeswoman.

Pressure built up beneath the street and dislodged the manhole covers, she said.

People could feel the initial blast a block away at the Allegheny County Courthouse.

No one was injured, according to Public Safety Director Lee Schmidt.

Officials were monitoring other manhole covers and coordinating with Duquesne Light to shut off power, Bourne said.

The utility said a low-voltage cable “failed,” dislodging the manhole covers and producing smoke and flame.

Outbound lanes of Grant Street heading toward the Strip District were closed for one block between Sixth and Seventh avenues. Inbound traffic was flowing.

One lane reopened as of 10:20 p.m. It was unclear when the road would be fully reopened.

While Duquesne Light said repairs were complete on Wednesday afternoon, it cautioned that traffic would remain restricted while”final physical adjustments” to the manhole covers were made.

Peter Rubash said he was working on the fifth floor of the Koppers Building when the noise startled him.

“It scared the hell out of me,” he said. “It was a huge blast.”

Rubash said he saw a flame jump from the manhole.

Smoke was pouring from one of the manholes in front of the U.S. Steel Tower between Sixth and Seventh avenues.

A second manhole cover made a popping sound just after noon, jumping up slightly from the road.

Officers urged people to stay away from other nearby manhole covers.

Austin Fairbanks, 29, said people began to run as they saw smoke coming from manhole covers.

“It just shook everything,” said Fairbanks of Mount Pocono, Monroe County, who was staying at a nearby hotel.

He described the sound as a “sharp explosion, almost like thunder.”

Staff writer Justin Vellucci contributed to this report.

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