UPDATE - The highway is back open.
UPDATE (3:26 p.m.) - Caltrans says the highway is expected to reopen at about 10 p.m.
UPDATE (2:45 p.m.) - CAL FIRE says two fires burned a total of about 5 1/2 acres.
Both reportedly started along the side of the highway.
CAL FIRE says forward progress has been stopped and the fires are 20% contained.
12:50 p.m. - Highway 166 is closed in both directions near Tepusquet Rd. east of Santa Maria because of a brush fire.
The fire was reported just after 11:15 a.m.
Firefighters are at the scene.
The closure extends from the Highway 101 intersection to Perkins Rd.
Caltrans says motorists headed to or from the Central Valley should use Highway 58 as a detour.
It's unknown how long the closure will be in place.
This is a developing story and will be updated with new information as it becomes available.