A double-decker tour bus that witnesses said was driving "erratically" barreled into a busy Union Square intersection Friday, crushing cars and ejecting at least one passenger before ramming into construction scaffolding and downing power lines.
The open-top bus was operated by City Sightseeing San Francisco, a representative confirmed.
Officer Albie Esparza, a San Francisco Police Department spokesman, said five people were critically injured, three suffered moderate injuries and at least 11 others suffered minor injuries in the 3 p.m. crash at Post and Stockton streets.
Esparza said Cal-OSHA was responding to the scene and that San Francisco police would be investigating the cause.
According to San Francisco Fire Department spokeswoman Mindy Talmadge, witnesses said the double-decker tour bus was traveling "erratically" down Post Street. The bus first hit a bicyclist, causing life-threatening injuries. It continued toward Union Square and proceeded to hit six vehicles, trapping some motorists inside.
A man who said he witnessed the events told KRON-TV that he saw someone fly through the upper deck windshield and into the construction scaffolding before the bus crashed into it.
"All the electrical was also coming down," he said.
Firefighters had to access the top level of the bus to remove a critically injured man. KTVU-TV helicopter video showed them loading him onto a stretcher.
The driver also had to be extricated, Talmadge said, as did two others who were trapped under the bus.
The injured were taken to hospitals throughout the city.
"This is definitely a serious multi-casualty incident," said Talmadge, who could not recall a tour bus crash of this magnitude in 20 years with the department.
The bus -- providing tours that are a popular staple for San Francisco visitors -- reportedly was carrying about 30 passengers. Another double-decker tour bus was hit by the errant bus but appears to have suffered little damage, video from the scene showed.