Flames spread quickly and badly damaged a cluttered home in downtown Lafayette early Thursday, authorities said.
Firefighters found it challenging to enter the two-story residence, because of "a lot of debris," said battalion chief Whit MacDonald of the Contra Costa Fire Protection District.
The fire appeared to have originated on the ground floor, but reached the second story soon after firefighters arrived, said MacDonald.
One person escaped from the home without getting hurt.
The fire started at about 1 a.m. at the home, near Golden Gate Way and 2nd Street.
Roughly one hour later the fire was under control.
Firefighters have remained on the scene to extinguish lingering hot spots.
Contra Costa County Fire Protection District posted pictures of the fire on social media.
The Moraga-Orinda Fire Department assisted in putting out the flames.
The cause of the fire is under investigation.