The fire was reported at about 11:50 a.m. in one unit of a duplex at 160 Fourth St., Capt. Chuck Rangel said. It has since been controlled.
One firefighter suffered head and neck injuries when a ceiling collapsed, and another had a shoulder injury, Rangel said.
Both were taken to a hospital for treatment, Rangel said. Their injuries are not considered life-threatening.
Three people live in each of the units. No other injuries were reported.
The fire appears to have started in the backyard area but the cause remains under investigation, Rangel said.