ROCKLIN (CBS13) – 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.

READ MORE: Gov. Newsom Pardons Woman Sentenced To Life In 90s For Fatally Shooting Abuser

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

READ MORE: Kings Run Away In 4th, Top Heat 81-64 At California Classic

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

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

MORE NEWS: Father Drowns In Lake Berryessa While Trying To Save Son

Exactly what caused the fire is unclear at this point.