Watch: Tube 'machete' attacker 'tried to behead victim' before police arrived to Taser him
Police are now considering the attack to be a terrorist incident
A knife-wielding Islamist fanatic may have planned to behead a victim after launching a terrifying attack on Tube travellers, witnesses feared.
The crazed attacker beat a 56-year-old man unconscious before cutting at his neck during the incident at Leytonstone Tube Station in east London on Saturday evening.
A shopkeeper who witnessed the knife attack at Leytonstone Tube station has described seeing a victim begging for help on the floor as he was punched and kicked.
Police were called to the east London tube station on Saturday evening after reports that a number of people had been stabbed and a man was threatening others with a knife.
Scotland Yard said officers arrived at the scene within five minutes of the emergency calls and the 29-year-old suspect was restrained and arrested after police discharged a Taser.
Detectives are currently searching a residential address in east London after the "violent unprovoked knife attack", which is being treated as a "terrorist incident".
Graphic footage of the attacks later emerged online showing the knifeman appearing to slash a man in the throat, and blood pooled on the station floor.
Salim Patel, 59, who runs the station shop and saw the attack unfold, said: "I was just at the shop when the train arrived and people came off.
"I heard some shouting, but sometimes drunk people shout. Then I saw the guy attacking the victim, punching him so hard. The victim was screaming 'please somebody help me. Help'.
"Then the attacker started kicking him on the floor. I think the victim was unconscious, he passed out. Then the attacker took a knife out and started stabbing him as he lay on the floor.
"The victim did not shout anything. I think he was unconscious. The attacker was saying something, I couldn't hear what."
John Cryer, MP for Leyton and Wanstead, said: "It is really shocking. It's an appalling thing to happen - it is to any community but Leytonstone is a very mixed community and people live together here very peacefully. It is quite a happy place to be."
He said he did not want to speculate about the motive behind the attack, and said it is important to leave the police to investigate.
Asked about how the local community is reacting to the attack, he said: "The reaction is one of shock, but at the same time people are determined not to allow something like this to affect their daily lives and the functioning of the community, which is a peaceful and pretty happy place to be."
The knifeman, who was said to be wielding a machete, reportedly said "This is for Syria" after he launched the attack.
A 56-year-old man suffered "serious" knife wounds, Scotland Yard said, but his injuries are not believed to be life-threatening.
He was taken by the London Ambulance Service to an east London hospital where he remains in a stable condition.
A second man sustained a minor injury during the incident but did not require medical assistance, while a woman was threatened but not injured.
Mr Patel, a father-of-six, said he called the police and described how the man was Tasered.
"He fell straight down hitting his head," he said
"Then he tried to get up. He dropped the knife and one of the officers kicked it out of his way. Then they cuffed him.
"When I saw them I thought 'Thank God a police officer has arrived.
"It was scary but I didn't feel too in danger because I wasn't in his way."
The attack comes weeks after the Paris terror attack, which claimed the lives of 130 people, and just days after Parliament voted to extend air strikes and bomb Islamic State (IS, also known as Isil, Isis and Daesh) to Syria.
Commander Richard Walton, who leads the Met's Counter Terrorism Command (SO15), said: "I would like to thank everyone who has so far provided information to officers and to the Anti-Terrorist Hotline following this unprovoked violent knife attack last evening at Leytonstone Underground Station.
"As a result of information received at the time from people who were at the scene and subsequent investigations carried out by the Counter Terrorism Command (SO15), I am treating this as a terrorist incident.
"I am aware that there were a number of members of the public in the Underground station who filmed the suspect on their mobile phones during and after the attack and I would urge them to come forward and speak to us and share with us the filming that they carried out.
"I would continue to urge the public to remain calm, but alert and vigilant. The threat from terrorism remains at severe, which means that a terrorist attack is highly likely."
Detective Superintendent Jacqueline Sebire, from Waltham Forest, said: "This incident highlights the risks taken by our officers on a daily basis. When they are called to incidents such as these, they enter, not knowing what awaits them.
"I would like to take this opportunity to praise not only their bravery in confronting the man who was in possession of a knife, but also their quick response in providing first aid to the victim whilst offering reassurance to the many members of the public who were travelling through the underground.
"We will continue to provide a visible presence in the area if anyone wishes to ask for advice about personal safety. We also remain in contact with community groups and local partners."
London mayor Boris Johnson was briefed on the attack by Metropolitan Police Commissioner Sir Bernard Hogan-Howe.
"Whilst this is clearly a serious incident and the mayor's thoughts are with the victim, it would be inappropriate to comment further at this stage on what is an ongoing investigation," the mayor's official spokesman said.
"The incident, and the swift and professional response of the officers involved, remind us of the dangers faced by the police every single day in their efforts to protect Londoners and keep the city safe."