The incident began at about 5:30 a.m. when a westbound big-rig collided with two other vehicles near El Portal Drive, CHP Officer Sean Wilkenfeld said.
That caused the driver to lose control, and the big-rig veered across westbound lanes and crashed into the center divider. It came to rest partially in the eastbound lanes, Wilkenfeld said.
"It's actually perched on the center divide," he said at about 8:15 a.m.
The truck driver suffered minor injuries and was taken to a hospital, he said.
The crash caused the closure of two lanes on the westbound side of the highway and three lanes on the eastbound side, Wilkenfeld said.
Crews have removed the big-rig, but motorists are still advised to avoid the area for the entire morning commute.
Caltrans crews are on scene assessing the damage, and the fast lanes in both directions will likely stay closed as crews repair the center divider, Wilkenfeld said.
Wilkenfeld reminded motorists to slow down, because roadways are slick from the rain. He also noted that hazardous driving conditions are expected again during the evening commute, and advised drivers to leave work early or late if possible to avoid traffic.