An underground explosion occurred in University City Thursday morning while work was underway to repair electrical lines.

The blast occurred around 10:15 a.m. near 34th and Walnut Streets on the University of Pennsylvania campus, according to the school's Division of Public Safety.

The explosion caused two manhole covers to burst into the air, authorities said.

One man was injured; further details about his condition weren't immediately known.

The underground Peco lines have been under repair for several weeks due to power outages.

"Rest assured that this incident is not related to the current international unrest," an alert to the Penn community said, referencing the terrorist attacks in Brussels this week.

Motorists should expect delays. The sidewalk in the area is closed.