San Francisco- Seventeen people were injured Monday night when a Municipal Railway bus swerved off Mission Street and crashed into an adult video store, police said.

One of the injured, a 60-year-old man, was in critical condition with head injuries.

The accident occurred at about 10:15 p.m. at Mission and Sixth streets when a 14-Mission double electric bus slammed into the Golden Gate Adult Superstore.

The cause of the crash was not immediately clear. Witnesses said the bus was eastbound on Mission Street when it veered off the road and onto the sidewalk at full speed. The front of the bus crashed through the wall and into the store, thrusting a streetlight into the second floor of the building, which houses several apartments.

San Francisco Police Lt. Greg McEachern said that three or four of the injured were taken to hospitals.

The driver of the bus was among the injured.

Passengers sat on the sidewalk amid shattered glass at the scene, awaiting treatment from paramedics. The intersection was completely blocked by the bus, which jutted out from the building into the road.

Police and passengers were at a loss to explain the crash.

“We were just going down the street and the next thing I knew, I flew to the floor. The bus swerved — nothing provoked it,” said 22-year-old Berkeley resident Kari Amu, who was at the back of the bus. “I don’t know what happened. We just hit the wall.”

“I was in the back of the bus. The next thing I know, I’m flying through the air,” said a man who declined to be identified. “It was a big bang. No brakes, we went full speed into the building.”