Updated 10/15/13 – 11:27 a.m.

CHICAGO (CBS) — Fire Department officials said a blaze that led to the partial collapse of an apartment building in Park Manor appeared to be the result of arson.

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WBBM Newsradio’s Bernie Tafoya reports Fire Department spokesman Larry Langford said investigators found traces of an accelerant in several areas of a two-story brick building in the 7300 block of South Vincennes Avenue. Langford said the building was under foreclosure.

Fire Department Deputy District Chief Dan Cunningham said gasoline cans were found inside the rubble.

“That’s all under investigation at this time,” Cunningham said.

The fire started around 1:15 a.m., and caused part of the building to collapse before fire crews arrived at the scene. A CTA bus driver called 911 after seeing the building burst into flames.

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More than 40 firefighters were dispatched to the scene to douse the flames.

“It looked like an explosion with extensive fire throughout the entire building,” Cunningham said.

Cunningham and Deputy District Chief James Mungovan said there were conflicting reports about whether or not anyone was in the building at the time. Some witnesses said a family with three children was inside, but fire crews were unable to search the building when they got there, due to the heavy flames, and the partial collapse.

“We were unable to conduct a complete and systematic search of the building, because of the collapse that was involved with the building. So, therefore, we had to fight this as a defensive fire from the exterior,” Cunningham said.

After the fire was extinguished, heavy equipment was brought in to sift through the rubble. Mungovan said cadaver dogs would be used to search the rubble and determine if anyone was inside.

As of 11 a.m., however, there was no sign that anyone had been inside the building when it burned. Langford said it’s unlikely anyone was inside.

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After the site is searched, it will be demolished, because it has become too unstable to be safe.