Guests at the Hampton Inn and Suites in south Napa were evacuated when smoke activated a fire alarm at 8 p.m. Sunday, the Napa Fire Department reported.

Napa Fire said the smoke was discovered to be coming from a locked guest room. Firefighters found a small fire in a bathroom that had been partially put out by the automatic sprinkler system, Fire Capt. Steve Becker said.

The cause of the fire is under investigation.

Guests were able to return inside after 90 minutes, Becker said.