By Cherri Gregg

PHILADELPHIA (CBS) — Police are investigating a suspicious fire that forced more than a dozen people from their homes overnight in South Philadelphia.

Flames broke out around 3:30 a.m. Sunday at a three-story vacant building that was under construction near Juniper Street and Synder Avenue.

Officials say the initial call came in as a trash fire — and when they arrived on scene heavy flames had already engulfed the first and second floors.

The fire quickly grew to three-alarms and spread to neighboring homes along the 1300 block of Snyder Avenue.

It took close to 100 firefighters about two hours to bring the blaze under control.

“We had a lot of heat on those exposures that we wanted to make sure we could save those properties,” said fire commissioner Derrick Sawyer. “If not, we would have lost four homes today. Because of the good work, they have minor fire heat and smoke damage, so that was the biggest challenge. We didn’t want those homes to be destroyed.”

Officials called the fire suspicious, but did not immediately rule it arson.

“I heard broken glass, and then I (saw a man) enter the building which caught on fire, and then I saw another gentleman on the roof right next to where the fire took place,” a witness told investigators. “Maybe five minutes later, the guy came running out, and about two minutes after he came out of the property there was a huge explosion.”

Authorities say a person of interest was caught fleeing the scene of the fire and was being questioned by ATF officials. Investigators were also looking at surveillance video from the area.

Fifteen adults and two children were displaced by the blaze. A Red Cross shelter was set up for those residents.

No injuries were reported.