SACRAMENTO (CBS13) – Firefighters battled a three-alarm warehouse fire in south Sacramento overnight.

The fire broke out on Wilbur Way off Elsie Avenue after 1 a.m. this Monday. Crews arrived to find heavy flames coming from the boarded-up warehouse.

READ MORE: Memorial Service For Fallen Marine Sgt. Nicole Gee Held In Roseville

The fire quickly progressed, causing firefighters to pull back and attack the fire from outside the building. They also carried out aerial attacks.

READ MORE: Suspect Armed With An Ax Arrested In Stockton

The cause of the fire is unclear, but there’s a chance the building may have been occupied by squatters.

MORE NEWS: Antelope Woman's Stolen Cotton Candy Trailer Located In Rio Linda

At one point, firefighters thought the roof would collapse.