Fire crews are at the scene of a brush fire Sunday morning in the Byron area that has burned about 40 acres, Cal Fire said.
The fire was reported about 9:20 a.m. in the 7900 block of Vasco Road, on the border of Contra Costa and Alameda counties.
The California Highway Patrol closed Vasco Road at Camino Diablo to due to heavy smoke from the blaze and issued a Sig-Alert for the area.
Cal Fire is responding with air and ground crews, according to a post on social media. Fire officials said there are currently no structural threats.
Information about containment or how the fire was sparked was not immediately available.