ATLANTA -- Georgia Power crews continued working Monday afternoon to repair underground power lines in downtown Atlanta that exploded overnight, sending manhole covers flying into the air.

The blast and the work to repair the damage prompted authorities to restrict morning traffic in the area near the state Capitol while workers completed the job.

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The explosion, which happened around 1:15 a.m., was caused by an electrical line that supplies power to a traffic light caught fire before exploding, a Georgia Power engineer said.

Traffic was blocked on several lanes of Piedmont Avenue and Martin Luther King Jr. Drive as authorities investigated. No injuries were reported and the roads have reopened.

Atlanta police officers who were in the area summoned help after the explosion occurred, city firefighters said.

"Two APD officers saw a couple of manhole covers flying off and felt the ground rumble," said Battalion Chief Nish Willis, who added that fears of a possible terrorist attack prompted firefighters to take additional precautions. "Because it was near the Capitol and underground explosions are not typical, we notified Georgia State Patrol, the Capitol Police, APD and we've talked to some of the higher ups in the fire department."

Homeland Security officials were also called to the scene.

An official with Georgia Power said such explosions are not common.

"This is very, very rare," said Ken Lund. "We have very few problems with this type of thing. Obviously it can happen but it's very unusual."

The force of the blast sent three, 50-pound manhole covers into the air. Officials said the incident disrupted power to some downtown traffic signals and a communications facility for the Georgia State Patrol.

Channel 2 Action News reporters Alan Wang and David Bodden contributed to this report.