At least 13 people were killed in a fire at a residential building in Philadelphia on Wednesday morning. Seven of the victims are children.

The recovery effort is continuing Wednesday afternoon.

Firefighters answered the scene at close to 7:00 a.m. ET and discovered an intense fire on the second story of a three-floor apartment building, the Philadelphia Fire Department said on their official Twitter account. It took just under an hour to get the fire in check, the department said.

First deputy commissioner of the Philadelphia Fire Department Craig Murphy clarified that eight people managed to escape from the building, with two being taken to a hospital.

“I’ve been around for 35 years now and this is probably one of the worst fires I’ve ever been to,” Murphy said. “We plan on making sure that this tremendous loss of life did not happen in vain.”

The cause of the fire is still unknown and being investigated.

“This is without a doubt one of the most tragic days in our city’s history, the loss of so many people in such a tragic way,” Mayor Jim Kenney said at a news conference. “Losing so many kids is just devastating.”