Chief Superintendent Chris Casey of the British Transport Police (BTP) said it may be “some time” before officers could give more details on the incident.
He added that it would “not be appropriate” to speculate on why the attack happened.
‘He collapsed on the floor’
The attack is understood to have started shortly after the Doncaster to King’s Cross train left Peterborough station.
One man who was on the London North Eastern Railway train told Sky News he saw someone coming though his carriage saying: “They’ve got a knife, I’ve been stabbed.”
“They were making their way through the carriage to get away from the suspects. They were extremely bloodied,” said the man who gave his name as Gavin.
He said by the time the train pulled up “they were basically on the floor”.
“That person ended up collapsing on the floor. They were taken to an ambulance pretty much straight away,” he said.
Gavin said passengers were ushered out into the station and “there were multiple people who had been stabbed making their way down”.
But he said one of the suspects had also come off the train and was “running rampant as well”, and was “waving a large knife” before he was taken down by armed officers.
