PHILADELPHIA --

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Traffic and mass transporation in Center City are back to normal after several transformer fires closed down several blocks on Thursday afternoon.

Crews evacuated about 3,000 people from the Grant Building and One Center Square, an office complex at 15th and Market streets, after multiple underground explosions at about 1:50 p.m.

Fire officials said a PECO crew was conducting work in the area transferring power from one line to another when there was an underground cable malfunction.

"We felt the explosion. Nobody knew where it came from, but everybody started looking down the alleyway and that's when we started seeing the black smoke," said Warren Hurdle.

Hurdle heard and felt the five underground transformer explosions.

"I noticed the black smoke coming out of the manhole cover, so I called my building man, and said 'You better come down here, this building is on fire or underneath is on fire.' And then the second one went. The manhole cover went shooting up, flames coming out of the manhole cover," said one man.

The explosion blew off four manhole covers in the 1500 block of Ranstead Street.

"We were sitting there, eating lunch and all of a sudden we heard this, 'boom,' and it shook the building, and we went to look out the window, and the smoke was coming out -- green smoke," said a man who was eating lunch on the 26th floor of a building a few blocks from the explosion. "I thought a bomb exploded."

"It blew up -- green smoke everywhere -- and we were running down to the fire exits," said one woman. "There was smoke in the fire wells, green, heavy smoke."

Chopper 10 showed flames coming out of one manhole. Crews tried to hose down the flames erupting from underground.

Fire crews reported one person suffered a minor injury and was taken to an area hospital. It is not known if the injured person is a civilian or a firefighter.

PECO reported the explosions knocked out power to 400 customers. By 4 p.m., most of those customers had their power restored.