Two civilians sustained minor injuries in the four-alarm Mill Street blaze, which destroyed a ground-floor hair salon and all of the apartments in the building where it began shortly before 2:30 a.m.
One resident climbed out his second-floor apartment window before firefighters rescued him.
Three surrounding residences sustained varying degrees of damage, officials said.
"All of the buildings are interconnected and have common spaces for fire to travel,” Fire Chief Brian McDermott explained.
The cause wasn’t immediately determined.
Dozens of mutual aid firefighters joined their city colleagues in dousing the blaze within 90 minutes.
The main building collapsed and will have to be demolished. There was no immediate word on the condition of the other buildings.
The American Red Cross was providing temporary shelter, food and clothing for those who were displaced.
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