Crews responded to black smoke and reports of an underground explosion in Center City Thursday afternoon.
Thick, black smoke could be seen coming from a manhole as SkyForce10 hovered above the area of 21st and Walnut Streets in Philadelphia before 6 p.m.
Video from the ground in the area showed smoke and flames emerging from underground.
PECO was called to the scene and officials confirmed the area was being evacuated.
PECO said 400 customers were without power due to the incident. By Friday morning that number was reduced to around 50 -- mostly residential customers by Friday morning, said PECO.
By Friday morning, the closure around the blast site was reduced to only the 2100 block of Walnut Street as crews used a jackhammer near the fire site.