Detroit fire crews are working to determine what sparked a blaze early Monday at an apartment building on the city’s west side that left at least 12 people hurt and displaced residents.

Officials remained on the scene near the 13000 block of Littlefield at 7 a.m. The flames appeared to have been extinguished and parts of the structure were charred. Authorities blocked off the front with yellow caution tape.

An emergency alert issued around 6 a.m. indicated a possible explosion.

Chuck Simms, the city’s executive fire commissioner, said the blaze was contained and the cause of what is being reported as an explosion is under investigation.

He said the department used drones with thermal imaging to confirm there are no other people in the building.

“We’re going to follow up with the hospitals to see how everyone is doing,” Simms said during a media briefing near the scene.

He said 12 people were taken to the hospital ― three in critical condition.

“Those were the ones who suffered burns,” the executive commissioner said. “They were in the same apartment and that’s where we are focusing our investigation.”

Simms added: “We allowed four residents of the building go in to get some of their personal belongings. They were escorted in by firefighters.”