The train was stopped at Huntingdon station in Cambridgeshire after police were called at around 7.40pm on Saturday.
A man wielding a large knife was shot dead by police with a stun gun after causing carnage on a high-speed train after leaving Peterborough station, police say.
British Transport Police said two people were arrested and a total of 10 people were taken to hospital, nine of them with life-threatening injuries.
Witnesses said the knife attacks began about 10 minutes after the train left Peterborough and passengers pulled their hazard lights.
Police declared the situation a “major incident” and said counter-terrorism police were currently investigating. At one point, “Plato” was announced, a code word used by British police and emergency services when responding to a terrorist attack, but was later cancelled.
