Dustin Hoffman has apologised over explosive allegations he sexually harassed a 17-year-old intern three decades ago.

Writer Anna Graham Hunter claims the Oscar-winning actor grabbed her bum and used vulgar language around her on the set of 1985 TV film Death of a Salesman.

"He asked me to give him a foot massage on my first day on set," Hunter alleged in a first-person account for The Hollywood Reporter.

"He was openly flirtatious, he grabbed my ass, he talked about sex to me and in front of me."