A crash involving a big rig on U.S. Highway 101 near South San Francisco caused a fuel spill and knocked out power to Caltrain overhead lines, authorities said.

The California Highway Patrol said the crash happened at just before 5 a.m. on southbound 101, just south of Sierra Point Parkway in Brisbane near the South San Franciso city limit. The trailer hit the railing along an overpass above the Caltrain tracks, rupturing the fuel tank and causing a diesel fuel spill, the CHP said.

The crash blocked the three right lanes of the highway, leaving only the left lane open. As of about 8:20 a.m., the big rig had been removed and the two left lanes were reopened, while the No. 3 and 4 lanes were closed so Caltrans could make repair to the damaged bridge.

A Caltrain spokesman said the collision knocked a fence onto the overhead power lines, causing the system to lose power from San Francisco to South San Francisco. 

Northbound trains were terminating at the Millbrae Transit Center until power was restored so riders could transfer to BART for the trip into San Francisco. 

At about 7:50 a.m., Caltrain restored power on the northbound track and began single-tracking through the affected area at reduced speeds, beginning with the northbound 503 and southbound 506 trains to and from San Francisco. Power to the southbound track was restored just after 10 a.m., and service resumed on both tracks, the agency said.  

The fuel spill totaled about 160 gallons, the CHP said. Details on the circumstances of the crash and any possible injuries were not immediately known.

As of 8:30 a.m., southbound Highway 101 traffic was backed up from Sierra Point Parkway in South San Francisco to the Interstate Highway 80 connector in San Francisco. At about 11:30 a.m., the CHP said Caltrans work on repairing the damaged bridge over the Caltrain tracks would continue, and the No. 3 and 4 lanes would remain closed until about 4 p.m.