The Metro Blue Line train was headed to Long Beach carrying about 230 passengers while the bus was out of service, Metropolitan Transportation Authority spokesman Luis Inzunza said.
Fourteen people from the train, including the operator, suffered minor injuries and were taken to local hospitals, Inzunza said. City Fire Department spokeswoman d'Lisa Davies said 15 people on the train sustained minor injuries. There was no immediate way to determine which casualty figure was correct.
The bus was being test-driven by a mechanic, who was not hurt.
"We had an out-of-service bus turn in front of the train," said Marc Littman, another spokesman for the MTA, which operates the train and the bus involved. "We don't know who had the right of way."
The impact knocked the front set of wheels from the front rail car about 12 inches off the track. The other cars remained on the track. Littman said they were still investigating the incident at the busy intersection.
The uninjured passengers were bused to the next station, six or seven blocks away, to catch another train, Metro spokesman Jose Ubaldo said. The track reopened about three hours after the crash.
The bus looked like it had been broadsided by the train, with a large dent on one side and a bend in the roof. The train showed much lighter damage.
Inzunza said the speed limit for trains in the area is 35 mph.
Chris Romero, 31, who lives in a small apartment near the tracks, said the screeching metal woke him up and he came running over. This crash, coupled with the recent Metrolink crash, has made him wary of taking the train.
"With everything that's going on, it's scary to go on the Metro," he said in Spanish through an interpreter, adding that he would not take the train "right now."
The crash comes one week after a Metrolink commuter train smashed into a freight train in the San Fernando Valley, about 30 miles northwest of downtown, killing 25 people and injuring more than 130.
MTA's popular light rail system includes the Gold Line to suburban Pasadena, the Red Line subway to Hollywood and the San Fernando Valley, the Blue Line to Long Beach and the east-west Green Line across communities in the southern portion of the county.
The Blue Line started service in 1990 and is the oldest leg of the light rail system.