These pictures show a topless man being arrested by police after he boarded a train with a knife.
Officers were called to Peckham, London, earlier today following reports of an armed man.
By the time they arrived at the location, the knifeman - believed to be in his mid-50s - had run onto a train.
Officers eventually caught up with the suspect and shot him with a Taser, before detaining him under the Mental Health Act.
Images from the scene show a man being taken along the train station platform by police officers - with a knife clearly visible in the hands of one of them.
A spokesman for the Metropolitan Police said officers were called to Queens Road in Peckham at 12.20pm today, however they found the man had fled in a car by the time they arrived.
There was a police pursuit before the man left the car and ran along railway lines to Queens Road Peckham Railway Station.
He was pursued by officers and a police helicopter was deployed to observe the chase.
The man then boarded a train - which was in service and contained passengers - still armed with a knife, a statement released by Scotland Yard said.
He was shot with a Taser and detained under the Mental Health Act.
Pictures taken by one passenger showed armed police on the railway tracks.
Alex, who was onboard the train, told Mirror Online: "I was sitting in the first carriage.
"We halted just before we arrived at Queens Road Peckham.
"The driver made the announcement to say there was a trespasser on the track.
"A few moments later he then announced that the trespasser had boarded the train onto carriage 2/3.
"He advised those who were in those carriages to leave them.
"People obviously freaked and ran to carriage 1. Myself and a few ran into the drivers section as he said as many as you can, can stay in here.
"The driver coped really well. He was calm and made sure we were all okay."
One witness who was on the platform with his girlfriend told Mirror Online the knifeman was shirtless and shouting about how “they weren’t going to get me this time”.
Detective Superintendent Nicky Arrowsmith added: "This incident highlights the challenges that police officers confront on a daily basis.
"I am very proud of the courage and determination of all the officers involved, and pleased that their work helped ensure no member of the public suffered any harm."
There are no reports of any injuries to members of the public or officers.