SAN FRANCISCO -- A bolt on the tracks may be to blame for a cable car accident Wednesday that sent five passengers and two car operators to the hospital.

At 10:18 a.m., an inbound Powell-Hyde cable car suddenly jolted to a stop at Powell and Washington streets, said Muni spokesman Paul Rose. Investigators later found the bolt lying on the track.

Rose said investigators are trying to determine where the bolt came from and it is unclear whether the bolt was part of the cable car track. Muni officials want to make sure the accident, which he said was a rare occurrence, never happens again.

Five passengers and two cable car operators were taken to a hospital with minor injuries. Updates on their condition were not available.

Bus shuttles are in place for riders on the Powell-Mason and Powell-Hyde cable car lines, Rose said. Regular cable car service is expected to resume Wednesday afternoon.

Bay City News Service contributed to this report. Contact Katie Nelson at 925-945-4780 or follow her at Twitter.com/katienelson210.