SAN FRANCISCO Seven people were injured Wednesday when a San Francisco cable car carrying about 40 passengers came to a sudden stop in the city's Nob Hill neighborhood, authorities said.
One of the injuries to an elderly man who fell and hit his head was considered potentially life-threatening, San Francisco fire spokeswoman Mindy Talmadge told The Associated Press.
Four other people were taken to a hospital with non-life-threatening injuries.
It appeared a 1.5-inch bolt stuck in the cable car's track caused the sudden stop, San Francisco Municipal Transportation Agency Director John Haley told reporters at the scene.
San Francisco police Officer Gordon Shyy said no other vehicles were involved in the accident, CBS Station KPIX San Francisco reported.
Officials believe the bolt doesn't belong to other cable cars that travel the route. Two other cable cars that passed safely through the site about 10 minutes before the accident were being inspected.
San Francisco Police Officer Mary Godfrey told KTVU-TV a female passenger suffered a leg injury when she was thrown from the cable car.
Transit agency spokesman Paul Rose also said the cable car conductor bit his tongue and suffered a concussion, and the grip operator injured his ribs.
Service resumed shortly before 2 p.m.