A police officer has been suspended after video emerged that appears to show him kneeling on a suspect's neck and head.
Footage filmed on Thursday in Islington, London, shows two officers holding a handcuffed man, who is black, on the pavement.
Deputy Metropolitan Police Commissioner Sir Steve House called the footage "extremely disturbing" and has referred it to the police watchdog.
Police confirmed they have charged a 45-year-old man with possession of a knife in a public place. In the clip, shared widely online, one police officer appears to be using his knee to control the suspect.
"Get off my neck," the handcuffed man on the floor can repeatedly be heard shouting. Eventually he is released from the ground and is seen talking to officers.
"I was worried he was going to get executed. That's just how George Floyd got killed," an eyewitness told the BBC. They continued: "If not for the crowds filming the police they could have suffocated him or broken his neck. He was on the floor and in handcuffs, what's the reason for a kneeling on his neck?"
In a statement, Deputy Metropolitan Police Commissioner Sir Steve House said: "The video footage that I have seen today and is circulating on social media is extremely disturbing."
He added: "Some of the techniques used cause me great concern - they are not taught in police training. One officer has been suspended and another officer has been removed from operational duty, but not suspended at this time. This decision will be kept under review."
Sadiq Khan, Mayor of London, said: "I'm deeply concerned about this distressing incident and we have raised this with senior officers at the Met Police as a matter of urgency.
"I welcome the fact the incident has been reviewed quickly by the Met and it's right that they have referred it to the Independent Office for Police Conduct (IOPC)."
According to the Metropolitan Police, the IOPC said it would conduct a full independent investigation.