The Saturday evening train to London was crowded but on time. Those heading to the capital had less than an hour left as it pulled out of Peterborough station, at shortly after 7.30pm.

But the unremarkable scene soon turned to horror, as bloodied passengers fled through carriages and sought refuge in toilet cubicles.

For many on the LNER Azuma train from Doncaster, the first indication that something was very wrong came in the form of an announcement over the train’s public address system.

“We are aware there is an incident … just keep yourselves safe,” a member of staff said. Given the season, others had initially assumed the commotion was a late Halloween prank.

However, the grim reality of a mass stabbing in a confined space soon became apparent, and by the time the train reached Huntingdon station, 10 people were being taken to hospital.

Among them was an LNER member of staff who heroically intervened in an attempt to stop the attacker.

While five other people had been released from hospital by Sunday evening, the man’s condition was said still to be life-threatening.

Detectives who reviewed CCTV footage from the train said it was clear his actions were nothing short of heroic and had “undoubtedly saved many people’s lives”.

Police later announced that a British man, 32, had been arrested on suspicion of attempted murder and remained in police custody. Another man, 35, was arrested but later released without charge.

Passengers and witnesses have meanwhile been recounting the 14 minutes of horror that occurred before an unscheduled stop at Huntingdon – 20 miles away.

Dayna Arnold became separated from her partner, Andy Gray, as people fled for their lives. She said she fell to the floor before pleading “please don’t” to the attacker as he stood over her with a knife.

She told the Daily Mirror: “I was running and when I looked back I saw the knifeman running after me. I fell down and I just said: ‘Please don’t kill me.’ Something shifted in his face and he just carried on. He said: ‘The devil is not going to win.’”

For Olly Foster, the bloody handprints left behind by those who had run through a carriage led to the realisation that something awful was unfolding.

“A guy suddenly ran past going: ‘Run, run. There’s a guy literally stabbing everyone and everything,’” Foster told the BBC. “At first there were a few of us looking at each other thinking it was a joke. Like it’s Halloween it might be pranking. But then you could kind of see in their faces they were being serious.”

He added: “By now, panic had broken out as passengers began streaming from the direction of where the attack was believed to have started.

“I put my hand on this chair, like just trying to push myself forward and then I look at my hand and it’s covered in blood.”

By now, passengers were hiding in the toilets and an emergency alarm had been pulled. In line with the standard protocols, the train would not come to a halt until it reached the next station.

For Foster, this “felt like forever”, as he stumbled across victims. They included an older man who was said to have deliberately got in an attacker’s way to shield a younger girl from the knife, sustaining injuries to his head and neck as he did so.

Another passenger, who gave his name as Gavin, told Sky News he had seen an “extremely bloodied” victim. “I was in coach G and there was quite a few people coming through. I had my headphones on but I heard one of the people coming through saying: ‘They’ve got a knife. I’ve been stabbed,’” he added.

That person collapsed on the floor, preventing Gavin and others from carrying on.

Elsewhere, Foster said he and other passengers had reached the end of their carriage, now even more panicked amid rumours that a gun was also involved. Amid a group of six, they were also attempting to stem the flow of blood from the head of the older man who was said to have saved the girl.

“We were just looking down the end of this carriage, just praying someone doesn’t walk down with a knife, with a gun,” he added.

By now, police were already scrambling after initial calls to Cambridgeshire constabulary at 7.39pm.

British Transport Police (BTP) were already on their way before the train pulled into Huntingdon station at 7.44pm after the driver switched to a slow track.

Within eight minutes of a call to BTP, two suspects had been apprehended by armed officers

Footage captured the moment armed police were seen running down the platform of the town’s small station, while a clip has also since emerged showing a man being Tasered.

Dazed passengers were filmed emerging on to the platform, at least one with a makeshift bandage wrapped around their waist and clutching a blood-soaked rag to their head.

Among them were supporters of Nottingham Forest travelling home after a match against Manchester United. Forest played tribute in a club statement, saying it was “aware that many individuals demonstrated extraordinary bravery which undoubtedly helped prevent even greater harm”.

A man could be heard shouting “kill me, kill me” as he was wrestled to the ground by police, according to one witness.

“Give me your hands now,” an officer shouted, as others held down the man and another officer ran over with a dog.

A passenger told Sky News: “He [the suspect] was waving a knife, quite a large knife, and then they detained him. I think it was a Taser that got him down in the end.”

On Saturday, the first word from the authorities that something had happened came at 8.47pm, when the BTP said on social media that they were “currently responding to an incident on a train to Huntingdon where multiple people have been stabbed”. At Huntingdon, emergency services arrived en masse.

“It felt like forever, but the train kind of stopped,” said Foster. Like other passengers, he had no idea where they had stopped and was initially reluctant to get off. “So I’m looking to my right and I just see 20 people in pure panic. There’s three people severely bleeding and one guy is holding his stomach, and there’s blood coming down his stomach, down his leg, and he’s just going: ‘Help, help. I’ve been stabbed.’”

Helping each other, but in some cases also staying together in groups for protection, passengers ran out of the station, not stopping until they had reached the car park.

By 10pm, the gravity of the incident was underlined in the form of a response from Keir Starmer.

The prime minister described it as “appalling” and “deeply concerning”, but, like others, was careful about his language. At one point earlier, police in Cambridgeshire had declared “Plato” – the national code word used by emergency services when responding to a “marauding terror attack” – but they later rescinded it.

Detectives are now looking at the suspect’s health history, and especially any mental health history, to try to establish a motive. Terrorism has been ruled out.

As dawn broke on Sunday morning, the Azuma train sat at Huntingdon station. Forensics officers combed the bloodied interior of the train as photographers and cameras were kept back behind a cordon that started at the car park.

Discarded debris – whether passenger belongings or medical kit wrappers – could be seen outside the door of the station.