Video footage posted online showed police in Manchester knocking a youth to the ground then striking him with a baton during Tuesday night's riots.

Greater Manchester police issued a statement saying the circumstances surrounding the footage were "currently unknown" and suggested the incident might be looked at by the force's professional standards branch.

In the footage posted on YouTube a group of police officers with batons and riot shields run towards a group of young men on bikes. A youth straggling behind the others dismounts from his bike and is knocked to the ground by an officer. Two officers then appear to strike him while he is on the ground. This lasts a few seconds and he gets up unaided. A helicopter is audible throughout.

The footage was uploaded by YouTube user nnix250, who wrote in a caption: "Taken at 10.15pm on August 9th, 2011, in Manchester. Tactical Aid Unit catch rioters trying to flee from the city centre, and blockade the street."

GMP said in a statement: "Police officers responding to incidents last night in Salford and Manchesterwere faced with extraordinary and unprecedented levels of violence being used against them. The professional standards branch is part of GMP's response in dealing with the aftermath of this critical situation. As the circumstances surrounding the footage of this particular incident are currently unknown, it is inappropriate for GMP to comment further."