SAN FRANCISCO—A San Francisco tour bus struck and seriously injured a pedestrian, who is in the hospital with "life-threatening" injuries.

The San Francisco Police Department said the accident occurred Sunday morning when the male pedestrian was struck while crossing a street in the city's mid-Market neighborhood.

Police didn't release the victim's name or the owner of the bus. The pedestrian, described as in his mid-60s, was rushed to San Francisco General Hospital.

The accident is under investigation.