A dramatic and stubborn fire erupted at a commercial building in downtown Los Angeles, prompting an early morning response from firefighters. The blaze began shortly before 5:30 a.m. at a single-story structure in the 1400 block of South Main Street. Firefighters arrived at the scene and were initially in defensive mode as massive flames and smoke emanated from the roof of the building, according to the Los Angeles Fire Department. Although firefighters seemed to have taken control of the incident by 6 a.m., flames were still visible in video from AIR7 HD. No injuries were immediately reported. The cause of the fire was unknown.