New York prison guards beat a handcuffed inmate hours before he died, a newly released video has revealed.

Bodycam footage of the incident shows three correction officers repeatedly kicking and punching Robert Brooks before leaving the prisoner unconscious in an examination room at Marcy Correctional Facility in Upstate New York.

In the video, which was taken on Dec 9, Brooks is repeatedly struck in the face and groin as he sits handcuffed to a medical examination table while other prison staff watch the assault take place.