A Rocklin warehouse was damaged in a fire early Thursday morning, authorities say.

According to the Rocklin Fire Department, firefighters responded to the Citrus Avenue building around 3 a.m. to investigate a water flow alarm. They then spotted smoke coming from the top of a roll-up door.

Firefighters had to force their way inside. Smoke was found down to the floor.

A sprinkler system managed to hold the fire until crews arrived, but firefighters say the building did suffer moderate damage – including a partial floor collapse.

Aside from that, it appears most of the damage is smoke related.

Exactly what caused the fire is unclear at this point.