A three-alarm fire swept through an apartment house in Portland, Me., early Saturday morning, killing five people and critically injuring one, in what the authorities said was the deadliest fire in the state in 30 years.

The fire broke out in one of the apartments of a duplex near the commuter campus of the University of Southern Maine, said Stephen H. McCausland, a spokesman for the State Department of Public Safety. The tenants held a Halloween party in the unit on Friday, he said. Seven people escaped without injury, but two or three people remained unaccounted for on Saturday evening, he said.

Mr. McCausland said the fire was the deadliest in Maine since a fire that killed five people in Hartland in 1984.

Firefighters responded to the fire around 7:15 a.m. at 20-24 Noyes Street, after receiving calls from several neighbors, Mr. McCausland said. None of the victims were believed to be students at the university, but officials would not know for sure until the bodies had been identified, he said.