SAN ANTONIO – An investigation is underway after a fire broke out early Thursday at a vacant apartment complex on the North Side.

San Antonio firefighters were called around 12:30 a.m. to Lee Hall Street near Interstate 10.

They arrived to find heavy flames coming from the building, which officials described as a series of “add-ons” with overlapping roofs, a design that made the fire difficult to contain.

Crews battled the stubborn fire for more than two hours before bringing it under control. No injuries were reported among firefighters or civilians.

The complex was unoccupied at the time, and investigators are working to determine what sparked the fire.