The incident happened on the 6.25pm LNER train from Doncaster to London Kings Cross just after 7.40pm yesterday (November 1).
Officers immediately attended Huntingdon station alongside paramedics.
Armed police from Cambridgeshire Police boarded the train and arrested two people in connection to the incident who have been taken to police custody.
Ten people have been taken to hospital with nine believed to have suffered life-threatening injuries.
One is being treated for non life-threatening injuries.
This has been declared a major incident and Counter Terrorism Policing are supporting the investigation.
Chief Superintendent Chris Casey said: “This is a shocking incident and first and foremost my thoughts are with those who have been injured this evening and their families.
“We’re conducting urgent enquiries to establish what has happened, and it could take some time before we are in a position to confirm anything further. At this early stage it would not be appropriate to speculate on the causes of the incident.
“Our response is ongoing at the station and will be for some time. Cordons are in place and trains are not currently running through the area, and there are also some road closures.
“I thank the public for their patience and their cooperation this evening which has already greatly assisted our policing response. We will update you again as soon as we have more information.”
Anyone with information who hasn’t already spoken to police is asked to contact BTP by texting 61016 quoting reference 663 of 01/11/25.
