A woman has been dragged to her death after her dog's lead became entangled in the doors of a train.
The woman boarded a Bay Area Rapid Transit (BART) train at San Francisco's Powell Street station with her dog at around 3pm on Monday.
The dog's leash was tied to her waist and, just as the doors were closing, she jumped off the train.
She cleared the doors but the dog and its leash did not.
As the train pulled away, she was dragged onto the tracks and killed.
The victim appeared to have been waving at someone moments before trying to get off the train, BART officials said.
She was identified by the San Francisco medical examiner as 41-year-old local resident Amy Adams.
The dog was not injured.
BART spokesperson Alicia Trost said: "This is a tragic loss of life, and we are following all safety protocols."
Police have spoken with witnesses and looked at video footage, and the National Transportation Safety Board is helping to investigate the death.
One witness, Mike Sim, said he had seen the woman being dragged and he had spoken with a hysterical man on the platform who said the woman was his girlfriend.
Mr Sim told KGO-TV that there was a blood stain down the platform "about an inch and half wide, all the way down".
Heather Griffin told Fox KTVU that she was commuting home shortly after the incident and met a woman named Angela, who was helping the dog.
"She just held onto the dog and got off at the next station. She said that the dog didn't have a collar or any tags on, that it was a German Shepherd and had a service dog vest."
According to BART, the trains run automatically unless the operator manually over-rides the door cycle.
The operator usually looks to make sure the passengers are clear of the doors but officials said Ms Adam got off the train just as the doors were closing - so after the operator's visual check.