“We’re conducting urgent inquiries to establish what has happened, and it could take some time before we are in a position to confirm anything further,” he said.

“At this early stage, it would not be appropriate to speculate on the causes of the incident.”

Paul Bristow, the mayor of Cambridgeshire and Peterborough, said he had heard of “horrendous scenes” during the attack, which began shortly after the train left Peterborough station. Passengers pulled the emergency alarm to alert the driver to the danger.

One witness described wounded passengers running through the carriages to escape the attack.

“They’ve got a knife, I’ve been stabbed,” one of the victims told other passengers during the mayhem, according to one witness who described the events to Sky News UK. This victim collapsed on the floor and was taken to an ambulance once the train came to a stop.

The witness described the victim as “extremely bloodied” from the knife attack. No explanation was given for the attack in any of the accounts in the immediate aftermath of the events.

“There were multiple people that had been stabbed who were making their way down [onto the station], but the suspect had also come off the train as well,” the witness said.

He added that he did not witness the attacks but saw some of the victims.

“The armed police were pointing to the suspect as he came off the train,” he said, adding that he was told the suspect was a male dressed “in all black” who was “waving a large knife” before being taken down.

The second suspect was then halted by police with what appeared to be a Taser, he said.

Another witness described the scene on the train as “horrific” and “pure chaos”.

“There was blood everywhere,” the witness told The Sun. ”It was a terrible scene, really violent. It was like something from a film. It didn’t feel real and just sparked pure panic on board.”

British Prime Minister Keir Starmer expressed concern about the “appalling” incident.

“My thoughts are with all those affected, and my thanks go to the emergency services for their response,” he said.

Home Secretary Shabana Mahmood confirmed the arrests and cautioned against conjecture about the incident.

“Two suspects have been immediately arrested and taken into custody,” she said. “I am receiving regular updates on the investigation. I urge people to avoid comment and speculation at this early stage.”