SAN FRANCISCO » A San Francisco transit bus and a commuter train crashed into trucks minutes apart Friday, injuring 40 people and sending more than 20 of them to the hospital, authorities said.

A San Francisco Municipal Railway bus and a dump truck collided at 1:29 p.m. in the Japantown neighborhood, leaving the bus with a smashed windshield. Twenty people were examined at the scene and a dozen of them went to hospitals, including one with serious injuries, fire spokeswoman Jennifer Balestrieri said.

Less than 10 minutes later, a Muni light-rail train collided with a tractor-trailer in the Bayview neighborhood. The train was derailed but its two cars remained upright.

Television reports showed the truck cab and trailer sitting at right angles, with the train squeezed between and its front pushed up against the cab.

Nine people were taken to hospitals with minor and moderate injuries, and 11 others were examined but declined to be taken to a hospital, authorities said.

Investigators told the San Francisco Chronicle that the big rig made an illegal left turn. However, the driver was not immediately cited, Officer Albie Esparza said.

Light-rail passenger Robert Williams said he suffered neck and shoulder pain.

Williams told the Chronicle that the train was full of passengers and had been slowing down as it pulled into a stop.

"The next thing you know, I heard a loud screech and the train came to a sudden stop," Williams said. "It was like an earthquake. Lots of people fell down."

Both accidents were under investigation.

A San Francisco light-rail train crashed into another city light-rail train in July 2009, injuring 46 passengers and the operators of both vehicles. Federal investigators concluded that the driver of one of the trains had lost consciousness.

Also Friday, a light-rail train collided with a van in Seattle, injuring five people. A 6-year-old boy was taken to a children’s hospital in stable condition while the others went to a hospital with minor injuries, KOMO reported.