A woman reportedly 'screamed' as she was sexually assaulted by a man during the morning rush hour at Ilford train station in east London on Tuesday.
Speaking to the Evening Standard, one witness said: "We were waiting to board the train and this guy molested her.
"She said, 'Stop it - I'm going to call the police.' He said, 'Go on, then,' and laughed.
"Everybody heard her screaming, but there were no staff on the platform. The train pulled out with that guy on it. No one helped her - not even other passengers.
"The girl was in a terrible state. She was shaking."
British Transport Police (BTP) has now issued an appeal for information.
A spokesman for BTP told Aol Travel: "We were called to Ilford station at 8.27am on Tuesday, 19 May, following reports of a sexual assault.
"Officers attended the station and spoke to a 33-year-old woman, who had been assaulted.
"No arrests have been made. Enquiries into the incident are ongoing."
Anyone with information is asked to contact British Transport Police on 0800 40 50 40, or text 61016, quoting reference 116 of 19/05/15. Information can also be passed anonymously to the independent charity Crimestoppers on 0800 555 111.
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