The incident was first reported at 7:47 p.m. on westbound 580 just west of Marina Bay Parkway.
The officer had been on the scene of an investigation into a two-car collision that occurred nearby at 6:52 p.m., when his patrol car was struck by another vehicle from behind, according to the CHP.
He suffered a head injury and was transported by helicopter in stable condition, according to the CHP.
A Sig-alert was issued for westbound 580 at 7:54 p.m., and a few minutes later the Sig-alert was updated to include both directions of travel.
Information about the officer's identity and current condition were not immediately available.
Update: I-580 Eastbound West of Marina Bay Pkwy Has Reopened to Traffic. Westbound Direction Remains Closed http://t.co/zNKXTVuEy0— 511 Bay Area (@511SFBay) July 23, 2015