NBC 10 tells us that crews are evacuating One Penn Center at 15th and Market after at least three underground explosions. Holy crap! PECO is on the scene, and police are shutting down roads in the area - for instance, the 15th Street exit of Vine Street has been shut down. If you know anything, leave us a comment or a tip.

UPDATE: ABC has more details. Sounds like it was an electrical problem of some kind caused when PECO was trying to switch circuits; their crews are trying to fix the problem now. Meanwhile, a number of buildings have been evacuated, many are experiencing power outages, and thousands of people are out on the street.