Some traffic is trickling by in both directions along the shoulder.
Wreckage from the crash is also blocking two of the westbound lanes coming off of the span into San Mateo County.
This all happened near the Foster City Boulevard exit from Highway 92 around 5:15 p.m.
The CHP believes one of the trucks is leaking diesel fuel, but officials do not know how much has leaked.
The crash is causing delays on northbound US 101 from Redwood City to the 92 interchange and on southbound 101 starting in Burlingame.