A Sig-alert was issued Wednesday night after a big-rig overturned on the Richmond-San Rafael Bridge, according to the California Highway Patrol.

The crash was reported just before 7 p.m. and initially blocked all lanes of Interstate 580. The far left lane re-opened about 8 p.m., the CHP said, but the right lane was expected to remain closed for several hours as crews worked to clean up the roadway.

The truck, which had an empty tank trailer, hit a concrete barrier, causing it to overturn, the CHP said.

The CHP advised motorists to use Highway 37 as an alternate route.

It was not known whether there were injuries involved.