The rally house at the rally site in Pittsburgh’s St. Clair Shores neighborhood was one of several properties that had been damaged or destroyed in the wake of the deadly rally.
The building is a popular destination for locals to gather in the evening for a weekend gathering of about 1,000.
The rally’s immediate aftermath was a series of explosions that knocked down many of the nearby homes.
People in the area told CBS News that many of them were lucky to escape serious injury, but others were hurt.
The National Guard is on the way to assist the city in finding and removing the rubble.
A spokesman for the National Guard said Thursday night that it was “aware of some incidents” in the neighborhood, but did not give details.
Police say at least two people have been arrested in connection with the fire.
Pittsburgh’s mayor, Bill Peduto, called the destruction a “terrible tragedy,” and urged the community to remain calm.
“We’re working hard to get everybody out of the rally house and get everyone back to their homes as quickly as possible,” Peduto said.
Police said they are still searching for witnesses, and are asking anyone with information to call them at 412-396-3612.
The Associated Press contributed to this report.