Update: All eastbound Bay Bridge lanes reopened hours after big rig overturns; Traffic at a crawl

SAN FRANCISCO -- An overturned big rig on the Bay Bridge Tuesday afternoon blocked multiple lanes of traffic in the eastbound direction out of San Francisco, grinding the evening commute to a halt for hours until it was cleared.

The California Highway Patrol said the crash happened around 4 p.m. on Interstate Highway 80 before Treasure Island and east of 4th Street and involved injuries.

The right and center lanes were completely blocked. All trucks were being asked to exit eastbound I-80 at 4th Street because there was not enough clearance to pass the overturned truck, the CHP said.

The cause of the crash was not immediately known, but wind gusts were measured as high as 70 mph on the bridge at the time of the crash.

"We don't know for sure, but we do suspect that the high winds on the bridge may have been a contributing factor to the truck overturning," CHP Officer Mark Andrews said.

People were advised to avoid the bridge and use alternative routes such as the Golden Gate Bridge and the San Mateo Bridge. 

Andrews told KPIX a tow truck was being brought from the East Bay, requiring a full if brief closure to all eastbound traffic. Once that tow truck arrived at the accident scene, authorities were able to reopen two lanes temporarily.

However, as of 7 p.m., Andrews said crews were awaiting a second tow truck in order to get the truck upright to remove it, a process that would require all lanes to be closed again during the process.

By 8:13 p.m., the second tow truck had arrived and the big rig had been uprighted, with two lanes open for traffic.

By 8:35 p.m., the CHP reported all lanes had been reopened. There was no immediate word on the nature of the injury or injuries.