Supt John Loveless says armed officers boarded the train and arrested two people within eight minutes of the 999 calls.
There are two men in police custody.
They are a 32-year-old male black British male and 35-year-old British national of Caribbean descent.
Of the nine people believed to have life-threatening injuries, four have since been discharged. Two people remain in a life-threatening condition.
BBC News - Nothing to suggest train stabbing attack is terror-related, police say - latest
There are two men in police custody.
They are a 32-year-old male black British male and 35-year-old British national of Caribbean descent.
Of the nine people believed to have life-threatening injuries, four have since been discharged. Two people remain in a life-threatening condition.
BBC News - Nothing to suggest train stabbing attack is terror-related, police say - latest