SAN FRANCISCO (AP) — Five people were injured Wednesday when a San Francisco cable car came to a sudden stop in the city’s Nob Hill neighborhood, authorities said.

One of the injuries — an elderly man who fell and hit his head — was considered life-threatening, San Francisco Fire spokeswoman Mindy Talmadge said.

Four other people were taken to a hospital with non-life-threatening injuries.

The cable car had about 50 passengers onboard.

San Francisco Municipal Transportation Agency Director John Haley told reporters at the scene that it appeared a 1.5-inch bolt stuck in the cable car’s track caused the sudden stop.

Additional details were not immediately available.