EMMAUS, Pa. - A fast-moving fire at an apartment building in an eastern Pennsylvania town left four people dead and the cause remains under investigation, police said Monday.

The blaze was reported around 11:50 a.m. Sunday at an apartment building in Emmaus, a Lehigh County borough about 60 miles northwest of Philadelphia, and quickly spread.

The bodies of four people were later found inside the building, according to Emmaus police Sgt. Todd Garloff. The names and ages of the victims weren't immediately released and it wasn't clear how they died. A police officer who responded to the fire suffered minor injuries, Garloff said.

The blaze sent smoke billowing into the air that could be seen for miles Sunday. Fire officials said the flames were so intense that they needed to pull firefighters out of the duplex for several hours.

"I made the decision, with the other chief officers, to pull everybody out - possible collapse," Emmaus Deputy Fire Chief Justin DeLong told WFMZ-TV.

The cause of the fire was under investigation and more information was expected to be released later Monday, Garloff said. On Sunday, police had said there were "several" victims who died in the fire, but that they weren't sure exactly how many.

The building had been a funeral home until the 1960s or 1970s, when it was converted into apartments.