A firefighter was seriously injured and two residents were hurt after a fire ripped through a mixed-use building in Clinton Hill early Monday morning. The fire broke out just after 3 a.m. at 504 Classon Ave., near Putnam Avenue, according to the FDNY. Fire officials say the flames started on the first floor of the three-story building and spread to the second floor. A deli located on the ground floor appears to have suffered heavy damage.

Video from the scene showed thick smoke rising above the neighborhood as firefighters worked to bring the blaze under control. The FDNY upgraded the response to a second alarm around 3:34 a.m., bringing 46 units and 141 fire and EMS personnel to the scene. Officials say one firefighter suffered serious injuries and was taken to a nearby hospital. Two residents were also injured. One person was treated at the scene and declined further medical attention, while another was taken to Brooklyn Hospital. By 5 a.m., firefighters remained at the scene as crews continued to check for hot spots and secure the building. The American Red Cross was also on site assisting people affected by the fire. It is not yet clear how many residents may be displaced. The cause of the fire remains under investigation.