Counter-terror police have now taken over the investigation as Scotland Yard confirmed the incident was being treated as a terror attack.
Videos from the scene purported to show bystanders tackling the suspect to the ground, taking his knife and pinning him down before police intervened.
The London Mayor Sadiq Khan confirmed that some of those stabbed have been "seriously injured" as he applauded the "breathtaking heroism" of bystanders "who literally ran towards danger" not knowing what it was they were faced with.