One man is in custody after multiple stabbings on a high-speed train in the UK that left a “heroic” rail staff member with life-threatening injuries, police have said.

A 32-year-old black British national has been arrested, British Transport Police (BTP) said, after the incident on Saturday night after which 11 people were treated in hospital. Another man, a 35-year-old Briton of Caribbean descent, who was also arrested was released without charge on Sunday, with police saying they had established he was not involved in the attack.

A “heroic” member of rail staff who tried to stop the attacker and “undoubtedly saved people’s lives” remained in a life-threatening condition in hospital on Sunday evening, police said.

Police said there was nothing to suggest the attack was a terrorist incident and have asked the public to come forward with any more information.

The man being held, after brandishing a large knife, is believed to have been shot with a Taser by police at Huntingdon train station in Cambridgeshire, eastern England.

BTP declared a major incident and initially said two people had been arrested after the train, the 6.25pm service from Peterborough to London King’s Cross in central London, was diverted and made an emergency stop at Huntingdon.

Supt John Loveless told reporters at the scene in Huntingdon on Sunday: “At approximately 7.42pm yesterday evening, there were calls to the police service in relation to multiple stabbings which took place on-board a train service.

[ Huntingdon train attack fuels growing fear in Britain of mass stabbings of strangersOpens in new window ]

“Officers immediately attended Huntington station alongside paramedics, where armed police officers from Cambridgeshire police boarded the train and arrested two people within eight minutes of the 999 call being made.

“Two men were brought into police custody, where they remain this morning.”

Eleven people had been treated in hospital and two remained in a life-threatening condition, while four people had been discharged, Supt Loveless said.

“Ten people were taken to hospital by ambulance and another person self-presented later that evening. While nine were believed initially to have life-threatening injuries, following assessment and treatment, four, thankful to say, have been discharged. However, two patients remain in a life-threatening condition.”

UK prime minister Keir Starmer called it an “appalling incident” which was “deeply concerning”, while King Charles said he was “truly appalled and shocked”.

The LNER train left Doncaster in South Yorkshire at 6.25pm. About an hour later, witnesses described scenes of panic on the train as bloodied passengers began to run through carriages warning others of the attack.

Olly Foster said he was in coach H when a man ran past warning passengers of a man “stabbing everyone, everything”.

“At first I thought: ‘Is it a joke, it’s Halloween, are they pranking?’ But you could see in their faces that this was serious,” he said.

Mr Foster said that as he moved through the train, he saw patches of blood on seats and a man who had been slashed in the head and neck while protecting a young woman from an attack.

Police said they received the first distress calls at 7.39pm and the train was forced to make an unscheduled stop in Huntingdon at 7.50pm.

Dozens of ambulances and police officers were waiting at platform 2 for the wounded and to apprehend the suspects, witnesses said.

UK defence secretary, John Healey, said there was “no reason for the rest of us not to get on with our lives”, as he described the early assessment of the mass stabbing as an “isolated attack”.

Viorel Turturica (42) a taxi driver who captured footage of a man’s arrest, told the Daily Mail that, shortly before, he was shouting “kill me, kill me, kill me” to the officers.

Mr Turturica said: “I had arrived at the station pickup point at 7.41pm and was waiting for a passenger. As soon as I see the passenger a few minutes later, I then see everybody running out of the station.

Britain’s home secretary Shabana Mahmood paid tribute to the bravery of staff and passengers on the train and confirmed the attack was not being treated as terrorism.

“We now know this attack is not being treated as terrorism, and that two British-born, British nationals have been arrested. The investigation is ongoing, and I am receiving regular updates from the police,” Ms Mahmood said. – Guardian/Reuters