Fresno County firefighters say the truck was hauling grapes and crashed near Parsons Road, which is a couple of miles west of Coalinga.
Authorities say the driver suffered minor injuries.
Caltrans has blocked the highway starting at Firestone Avenue. Officials say the road will remain closed until the debris is cleared. Drivers are advised to avoid the area.
The estimated time of reopening was not immediately available.
COALINGA AREA: Due to an overturned big rig, State Route 198 is closed in both directions of travel starting at Firestone Avenue.— Caltrans District 6 (@CaltransDist6) August 26, 2020
No ETO at this time. Seek alternate routes.@ChpCoalinga @CaltransD5 pic.twitter.com/gUJgQ4vUot