KNOXVILLE, Tenn. (WATE) — Crews with the Knoxville Fire Department worked an early morning house fire Thursday in the 1500 block of North Fourth Avenue. The house was unoccupied at the time of the fire.

According to KFD, at 4:03 a.m., the Knox County E-911 Center received a call reporting a house fire and the caller advised that the neighboring vacant house was “fully involved,” a news release states. Arriving KFD crews found heavy fire coming from the front of the house and immediately made an aggressive attack on the fire.

They protected the neighboring property and the fire was declared under control by 4:30 a.m. KFD says crews remained on the scene in order to cool hotspots throughout the remaining structure. The house sustained “very heavy fire damage.”

KFD fire investigators are working to determine the cause.