LOS ANGELES, California (CNN) -- More than 100 Los Angeles-area firefighters are battling a large fire on a back lot at Universal Studios, fire authorities said. Filming may have been going on at the time the fire broke out early Sunday on the Universal Studios back lot. There were also reports of an explosion in the studio's adjacent amusement park, said Los Angeles County Fire Capt. Frank Reynoso. The three-alarm blaze began about 4:45 a.m. PT (7:45 a.m. ET) Sunday and reportedly damaged two "prop" buildings, including a chapel, and a popular ride called the "Cyclone," Reynoso said. "It will be awhile before we have it under control," he said. Television footage showed the blaze burning through the roofs of structures at the park and large plumes of smoke. Firefighters were dropping water on the blaze from helicopters. Watch footage of copters trying to douse the huge fire » "We don't know what the cause of this is," Reynoso said. Reynoso said he heard reports that filming may have been going on when the fire broke out.