A firefighter suffered minor burn injuries at an apartment fire Tuesday night after an incendiary device was allegedly lit and thrown into a living room at the Fresno Square Apartments on Cedar Avenue, Fresno Fire Department reported.

Fresno Fire Capt. Reggie Zellous said the first crew arrived at the fire southwest of Fresno State at 11:26 p.m. When firefighters arrived on scene, there was heavy smoke and flames in the living room of one unit.

“Someone said that someone threw a Molotov cocktail through one of the bottom apartments,” Zellous said. “They heard a loud sound, they looked up, and there was fire in their living room.”

Another fire chief arrived and found flames coming from the rear of the apartment and extinguished them. The blaze took 10 to 15 minutes to control, Zellous said.

Two units were completely gutted, and a third adjacent unit was damaged.

The units were occupied, though Zellous couldn’t say by how many people. Red Cross responded and assisted the occupants with housing arrangements.

Though none of the occupants were injured, paramedics treated one firefighter for minor burn injuries on his left forearm.

The fire is considered arson, Zellous said, and Fresno Police Department was on scene to assist in the investigation. Cedar Avenue between Shaw and Santa Ana avenues was blocked off afterward for the investigation.

Firefighters were able to contain the fire within 10 to 15 minutes. Zellous said there were no sprinklers in the unit, and it was not apparent that any smoke alarms went off.

Zellous said a suspect was not identified, and the investigation was ongoing.