A fire broke out Saturday night in a compost bin on the third flood of the Riverfront complex on Main Street and was promptly extinguished by an automatic sprinkler, the Napa Fire Department reported.

The incident prompted a brief evacuation of the Morimoto restaurant on the first floor as water cascaded down the outside of the building.

Fire officials said the fire was confined to the compost toter, which was located in a trash room, and damaged none of the upper floor residences.

The cause of the fire is under investigation.