The fire broke out at a home at 23 Lithgow Street in Dorchester around 3 p.m., the Boston Fire Department said on Twitter.
Upon arrival, crews found flames coming from the back porch of the home. The fire had also spread to the neighboring building at 19 Lithgow, the department said. Shortly after, the back porch collapsed and the fire was elevated to a third alarm.
One firefighter was taken to a local hospital with minor injuries, the department said. The cause of the fire remains under investigation.
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