FRESNO, Calif. (KSEE/KGPE) - A fire at a vacant commercial building in Fresno sent a large plume of smoke up into the sky Tuesday morning. The Fresno Fire Department says just before 8 a.m. they responded to South East Avenue, near Florence Avenue, for a reported structure fire. As crews arrived they reported smoke and flames pouring out of a vacant commercial building. As they worked to extinguish the fire, a portion of the roof began to collapse. Due to the condition of the building, firefighters say they were forced to defensively fight the fire from the exterior. Investigators say the building is known to have a lot of homeless activity and is believed to have been ignited by an unattended fire.