Two people are likely dead after row homes in South Philadelphia collapsed from a raging fire Thursday, the fire chief said.

"We have pretty good confidence that there are two people who are missing and presumably deceased," Fire Commissioner and Emergency Management Director Adam Thiel said Thursday evening, according to NBC Philadelphia.

A number of row homes were involved in the three-alarm blaze. Three completely caved in and two were severely damaged, according to the Philadelphia Fire Department. Authorities had initially said at least two people were trapped after the roof of one home fell in.

"They actually were able to locate someone, but that individual was trapped under so much debris that they were not able to extricate them," Thiel said.

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Police said they received calls reporting a house explosion and the smell of possible gas just after 11:30 a.m.

Thiel said Thursday afternoon that the situation was still dangerous even though the fire was under control.

A witness, Austen Travis, told NBC News that neighbors ran toward the fire and saw what appeared to be a woman trapped in the debris.

"I was in the area about 30 minutes after it happened, and police had started blocking everything off, but all the streets for four to six blocks around were completely choked with thick smoke," Travis said.

Authorities worked to extricate two people trapped in a collapsed home in South Philadelphia. Philadelphia fire dept.

Crews were putting out pockets of fire, and Thiel said he could not rule out that other people might be in the rubble, NBC Philadelphia reported.

Pennsylvania Gov. Tom Wolf tweeted that he was in touch with Philadelphia's mayor and said he had offered state assistance if necessary. He said he was "deeply saddened to learn of the potential loss of life and wishing for the safety of all residents and first responders."

Police said the cause of the fire was unknown.

Philadelphia Gas Works was working to cut off gas to 10 adjacent properties as firefighters battled the flames, the company said. Three gas work crews were on the scene to help authorities.

Aggressive winds were blowing at 12 mph when the fire began, according to NBC Philadelphia.