A knifeman chased and threatened terrified bystanders after stabbing a passenger on a train, witnesses said.

Police swarmed on Forest Hill station after the "horrific" attack at about lunchtime. A 38-year-old man was arrested on suspicion of GBH.

A man in his 40s was taken to hospital with stab injuries where his condition was described as serious but not life-threatening.

Passengers fled the station screaming with terror after the armed man reportedly shouted threats at people on the scene in south London.

Witnesses said there was a huge presence of emergency services at the station as they warned people to avoid the area as the attacker was "ranting on the streets".

Juliette Cooper, 39, was jogging near the station when she heard screams.

She said: “I spoke to my daughter’s friend who was on the train and she said a man with a knife was going around and stabbing people

“She said everyone literally ran off the train at Forest Hill where he got off as well.

“He had a wild look in his eye."

Another woman said said dozens of passengers fled the station as she arrived at Forest Hill at around 1.30pm.

She told the Standard: “Around 30 people were running out of the station screaming. There was a guy there pacing around and shouting ‘I’ll take everyone on’.

“I asked people what had happened and they said he had stabbed someone with a knife. I called the police."

A British Transport Police spokeswoman confirmed officers were called at 1.18pm following a serious assault and that a man was arrested on suspicion of GBH.

He remains in police custody.

A man in his 40s is in hospital with stab wound injuries but his condition is not life-threatening, police said

Senior investigating officer Det Chief Inspector Paul Langley said: “This was a serious assault on a man in broad daylight and we are aware that other passengers may have seen what happened or been threatened themselves.

“We have spoken with many witnesses from the train but if you saw what happened and haven’t yet contacted police, please do so as soon as you can.”

Police added the attack was not being treated as "terror-related".

A London Ambulance Service spokeswoman said: “We were called at 1:16pm to reports of a stabbing at Forest Hill Railway Station.

“We sent a single responder in a car, an ambulance crew and an incident response officer to the scene. London’s Air Ambulance was also dispatched.

“We treated a man at the scene and took him as a priority to hospital.”

Did you witness this incident? Contact our news desk on 0203 615 2500 or news@standard.co.uk