The closure was caused by a big-rig accident, Officer Peter Van Eckhardt said.
No one was reported injured in the accident but the truck's oil tank was punctured and crews are on the scene cleaning up the spillage, Van Eckhardt said.
The Sig-alert was issued shortly after 4 a.m.
The truck had been removed from the scene by 5 a.m. but the CHP does not expect all lanes to be reopened until at least 7 or 8 a.m. due to the clean up effort, Van Eckhardt said.
Motorists are advised to expect delays.