AUSTIN, Texas — Investigators suspect arson caused a three-alarm fire that destroyed an abandoned apartment building on South Lamar Boulevard early Saturday, causing an estimated $4 million in damage.

Firefighters were dispatched around 3:30 a.m. to 2119 S. Lamar Blvd., where the structure was already fully involved on arrival, with flames coming from throughout the building. Crews quickly shifted to a defensive strategy as portions of the structure began to collapse, according to the Austin Firefighters Association.

Incident command upgraded the response to a third alarm, bringing the total number of responding firefighters to more than 80.

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No injuries were reported. The building was unoccupied when crews arrived.

Firefighters remained on scene for several hours, battling hot spots while working to protect neighboring homes and businesses.

The Austin Fire Department said that evidence gathered during the investigation points to arson as the cause. Damage is estimated at $4 million. The investigation is ongoing.