Passengers fled in terror as a person was assaulted on the platform of a busy Tube station in London.
Forensic officers were seen at Marble Arch station after the incident on Friday afternoon.
Terrified witnesses said they heard screaming from the Central line platform as people fled the scene.
Footage showed police officers combing the scene for information as the station was shut for several hours after the incident.
One witness, named only as Abi, 31, told GetWestLondon: "It was incredibly scary, it really was terrifying - I’ve lived in London 11 years and never seen anything like this before.
“I was on the westbound train which pulled into Marble Arch.
"The doors opened and pretty soon after there was loads of screaming coming from the other platform and lots of people ran away from the commotion.
"I couldn’t hear anything there was so much screaming and the alarm went off on the train, which I assume is because someone had pulled it."
Police confirmed one man had been detained but did not provide further details on the victim's condition.
A British Transport Police spokesman said: "Officers were called at 3.10pm today after reports of an assault at Marble Arch Underground station.
"Officers and the London Ambulance Service attended the scene.
"A man has been detained as part of our investigation into the incident."
Marble Arch station reopened shortly before 6pm, Transport for London said.
Anyone with information should contact police via text on 61016 or call 0800 40 50 40, quoting 344 of 27 April.
