Several dozen people were injured when two US light-rail trains collided, authorities said.
Forty-four people were taken to hospitals – three with what appeared to be severe injuries – when a San Francisco Municipal Railway train crashed into the back of another near a boarding platform, officials said.
“This is probably one of the largest casualty incidents in recent years (in San Francisco),” said Pat Gardner, a deputy chief with the San Francisco Fire Department. Mr Gardner said about 40 rescue workers were at the scene.
Witnesses said the westbound train barrelled into the other one as it emerged from a tunnel connecting downtown San Francisco to the city’s western neighbourhoods.
The trains were full. The front of the first train was smashed, while the second train did not appear to suffer major damage. The operator of the first train was among the three who were seriously injured.
Several people sat bloodied and bandaged near the crash scene as rescue workers isolated the most severely injured.
Mr Gardner said 20 people suffered moderate injuries. He described another 21 people as “the walking wounded”.
The cause of the crash was under investigation.
Judson True, a spokesman for the San Francisco Municipal Railway, said investigators will look at “mechanical and human issues”.