The Metropolitan Police is conducting a review into an incident involving an officer detaining a black teenager.
The video of the arrest on Heath Park Road in Romford on Monday is circulating on social media, resulting in online comments suggesting excessive force being used.
An onlooker can be heard in the film saying: "You can't just hit him like that".
Police have confirmed that officers on patrol on Monday stopped and searched two teenagers under the Misuse of Drugs Act. A police statement says that after a struggle one male, aged 17, was detained.
The video, appears to show the teenager being struck at least twice with a baton while he shouts at the officer to stop and that he is a child. The teenager appears to be handcuffed.
A referral has now been made to the Independent Office for Police Conduct.
The Metropolitan Police spokesperson said: