Police say a fire that badly damaged a residential heritage building in Halifax’s south end is being treated as suspicious.

Neighbours say they heard an explosion before 2:30 a.m. Tuesday and police and fire crews responded to the building on Inglis Street a short time later.

“I’ve heard reports from residents in the building, from other workers in the area, that they heard a bang,” said Deputy Fire Chief Roy Hollett. “But we still don’t know, was the bang a result of the fire, or did the bang cause the fire?”

By the time crews arrived on scene, the fire had spread to all three floors of the Victorian-era building, which contains 15 condominium units in three separate wings.

About 25 people have been displaced by the fire. They all made it out safely and no injuries were reported.

Investigators have determined that the fire started outside at the back of the building, but inspectors haven’t been able to identify an exact cause.

“We look at cigarette butts as a potential ignition source, electrical, motor, something that would cause a fire, and in this case there’s nothing back there, so for us it goes right now undetermined, and the fire we’ll say is suspicious and we’ll turn that file over to police,” said Hollett.

The fire on Inglis Street was the second to break out in the area in a matter of hours. A fire started at the back of an apartment building on South Street, just a few blocks away, around 11:30 p.m. Monday. The building sustained minor damage.

“We’re not confirming they’re connected or anything but we’ll look into all angles and anything that comes forward,” said Halifax Regional Police Const. Carol McIsaac.

Hollett said they haven’t confirmed whether the fires were deliberately set, but he has asked for a review of both fires.

“We look at any potential trends, we look at everything to see if there’s a trend of fires outside, and if we feel something is unusual or suspicious, then we’ll connect with other agencies,” he said.

The review will examine similarities between the two fires, including the fact that they were both started outside, investigators haven’t been able to determine the ignition source, and they happened in the same area overnight.

An update is expected before the end of the week.

With files from CTV Atlantic's Marie Adsett