In a statement, the Brititish Transport Police said:
"A four-year-old girl, Emma Lifsey, sustained serious injuries and was airlifted to Sheffield Children's Hospital, where she was sadly pronounced dead in the early hours Wednesday, 5 December. Her family have been notified.
"The police investigation into the incident is ongoing and remains very much in the early stages. Officers are working hard to establish the full circumstances surrounding the incident, including how the vehicle came to be on the tracks at the time."
More top news
It will be warm and sunny in much of the UK with a risk of heavy, thundery showers for parts of central and southern England and Wales.
Ariana Grande, who had been performing at the Manchester Arena when the bombing happened, tweeted a message of support for those affected.
Berlinah Wallace was convicted of throwing a corrosive substance with intent but acquitted of murder.