4 injured in SF chain-reaction crash involving 2 AC Transit buses

Police investigate a traffic collision involving two AC Transit buses and at least one passenger vehicle at Folsom and Fremont streets with one of the buses coming to a stop on the sidewalk in San Francisco, Calif. on Wednesday, Sept. 27, 2017. The Fremont off-ramp from the Bay Bridge is closed for several hours while the investigation continues. less Police investigate a traffic collision involving two AC Transit buses and at least one passenger vehicle at Folsom and Fremont streets with one of the buses coming to a stop on the sidewalk in San Francisco, ... more Photo: Paul Chinn, The Chronicle Buy photo Photo: Paul Chinn, The Chronicle Image 1 of / 4 Caption Close 4 injured in SF chain-reaction crash involving 2 AC Transit buses 1 / 4 Back to Gallery

An out-of-control AC Transit bus crashed into several vehicles, including another bus, in downtown San Francisco Wednesday morning before jumping a curb and careening down a sidewalk, officials said.

At least 4 people, including the driver of the AC Transit Transbay Express bus that started the chain-reaction wreck, were injured and taken to hospitals, said Officer Robert Rueca, a spokesman for the San Francisco Police Department.

The incident occurred about 9:22 a.m. at the intersection of Fremont and Folsom streets, near the temporary Transbay Transit Center.

The green AC Transit bus crashed into the rear of another AC Transit bus making a turn onto northbound Fremont. The green bus slammed into other vehicles in the area before jumping a curb and traveling about 100 feet on the sidewalk, taking out shrubbery and knocking over a light pole, according to witnesses and police.

The bus finally stopped when it crashed into scaffolding at a building in the 200 block of Fremont Street.

Rueca said those injured were on the bus, and that no one on the sidewalk at the time of the crash was hurt.

Construction worker Chad Preston, who was working in the area, said he saw the crash and immediately ran over to help. He said passengers were climbing out the windows of the green AC Transit bus and that the driver, a woman, was initially unconscious.

The cause of the crash is under investigation and the area was closed to traffic.

Steve Rubenstein is a San Francisco Chronicle staff writer. Email: srubenstein@sfchronicle.com Twitter: @SteveRubeSF