The 5 Freeway was closed in both directions over the Grapevine pass as a snow storm swept through the region Wednesday night.
Heavy snowfall resulted in several vehicles stuck on the roadway between Lake Hughes and Grapevine road, California Highway Patrol said.
Authorities warned drivers of possible delays and road closures throughout the region, including through the Grapevine and the Cajon Pass Wednesday and Thursday.
The National Weather Service issued a winter storm warning for the mountains of San Bernardino and Riverside counties from 6 p.m. Wednesday to 6 a.m. Friday, and to 10 p.m. Thursday for the L.A. County mountain areas.
"Travel will be very difficult to impossible, including during the morning commute on Thursday," the weather service said in the alert, warning of possible toppled trees and piles of snow measuring up to 30 inches at the highest peaks.
Elevations above 3,000 feet can get snow accumulations of up to 18 inches, with winds gusting at 45 mph in the Tehachapi and Fort Tejon areas, including along Interstate 5 through the Tejon Pass.
One lane of the 5 Freeway was closed from Halsey Canyon Road to Parker Road through the Grapevine at 7 p.m. before all lanes were closed in both directions at about 10:30 p.m., according to Caltrans.
California Highway Patrol said officers were escorting traffic over the Grapevine as snow fell on the roadway, creating dangerous driving conditions.
The snowy conditions along the freeway are expected through 10 p.m. Thursday, according to the weather service.
"Road closures and travel delays are possible," the weather service said, adding that the roadways would be slick and covered with snow.
Highway 33 was closed by 8:30 p.m. due to snow blowing with near white-out conditions between the Wheeler Gorge Campground and State Route 166 in Ventura County.
Heavy snow could also affect traffic on Highway 14 and the Ortega Highway.
Up to two inches of snow are expected at elevations above 5,000 feet in Los Angeles County, excluding the Santa Monica Mountains.
CHP reminded drivers to plan ahead, slow down and check for alternate routes.
Officers will be escorting vehicles on the Grapevine pass before clearing the roadway.
It's unclear when the freeway will reopen.