Los Angeles - A week after the worst train crash in southern California history, another train was involved in an accident Friday morning, colliding with a bus in downtown Los Angeles.

But the casualty numbers were far lower than the 25 killed last week. According to police only 13 people suffered light injuries in the incident.

The collision occurred at around 6:15 am and the bus was not carrying any passengers. Officials said the collision caused the train to derail but it remained upright.

"We had an out-of-service bus turn in front of the train," said Marc Littman, spokesman for the Metropolitan Transportation Authority, which operates both the train and the bus. "We don't know who had the right of way."

Friday's collision is likely to further erode public confidence in the Los Angeles mass transit system which had been enjoying a resurgence in ridership in recent months in reaction to the spiraling prices of petrol.