US actor Will Smith slapped comedian Chris Rock in the face on stage during this year's Academy Awards ceremony.

Rock was presenting the award for best documentary feature at the Oscars in Hollywood on Sunday.

Smith stood up from his front-row seat and walked onto the stage to smack Rock in the face after the comedian made a joke referring to the appearance of Smith's wife, Jada Pinkett Smith.

Pinkett Smith is reportedly suffering from hair loss.

Smith later took to stage to accept the best actor award.

In his acceptance speech, Smith tearfully said he wants to apologize to the Academy and all his fellow nominees.