A normal day in Downtown Pittsburgh became a tense scene around noon on Monday after an underground explosion rocked the area. 

A wiring system from Duquesne Light malfunctioned and caught fire, causing the blast that blew out manhole covers along Grant Street, and caused thick, black smoke to billow from underneath.

Austin Fairbanks and his wife were visiting Pittsburgh from Mount Pocono, Pennsylvania, and were preparing to check out of the Drury Plaza Hotel. Fairbanks was leaving the hotel to pick up his car from the valet when he saw the scene along Grant Street.

"The initial explosion was like — it just shook everything," he said. "I mean, it was discombobulating, almost. It was just like 'What the hell was that?' for a second."

Attorney Steve Stallings told KDKA-TV he heard the sound in the Joseph F. Weis Jr. U.S. Courthouse at Grant and Seventh Avenue.

"We were in a jury trial across the street in the federal court on the eighth floor, and I heard an explosion," Stallings said. "I turned to my colleague and said, 'I think that's an explosion!'"

One of the pastors with the First Lutheran Church told KDKA-TV their building temporarily lost power after the blast, but then it recovered quickly. Within minutes, first responders closed down traffic on Grant Street between Sixth Avenue and Seventh Avenue. Crews from Duquesne Light were on scene soon after, and after the smoke cleared, they determined the source of the explosion, and the situation was under control.

The westbound lane on Grant was opened within a couple of hours, but the eastbound lanes remained closed as crews worked to repair the wiring that was damaged.

But for a matter of a few minutes, the scene was tense as witnesses tried to understand what they were seeing and hearing.

"I didn't know what it was, and I'm sure they didn't know either at the time, so everyone was just kind of on edge," Fairbanks said. "If they're on edge, I'm a little bit on edge, but once I saw them walking around the manhole, I was like 'All right, well they've got to be OK.'"

Pittsburgh Public Safety confirmed the faulty underground wiring as the cause of the fire, and no evacuated buildings or injuries were reported.