Will Smith hits Chris Rock on stage, then wins an Oscar

Best actor winner Will Smith smacked presenter Chris Rock in the face and shouted a vulgarity at the comedian for making a joke about his wife's hairstyle in a shocking moment overshadowing the Oscars ceremony on Sunday.

About 45 minutes later, when accepting his first Oscar for best actor for his role in King Richard, Smith apologised to the Academy of Motion Picture Arts and Sciences and his fellow nominees in a tear-filled speech, but not to Rock.

"I want to be a vessel for love," Smith said during his acceptance speech.

The episode upstaged the rest of the 3-1/2 hour show, and was sure to become one of the most memorable moments in 94 years of Academy Awards.

It may cost Smith his sterling reputation in Hollywood, but not a criminal charge, at least for now, as Los Angeles police said Rock declined to file a police report.

The incident began when Rock was roasting some of the nominees and made fun of Smith's wife, Jada Pinkett Smith.

"Jada, I love you. 'G.I. Jane II,' can't wait to see it," he said, referencing the 1997 film G.I. Jane in which actress Demi Moore shaved her head.

It was unclear whether Rock, a comedian and actor, was aware that Smith's wife suffers from a disease that causes hair loss.

But Smith quickly stood up and marched toward the stage to confront the comedian.

Rock had his hands behind his back when Smith threw an open hand at his face that produced an audible smack, and in a form befitting an action movie star. Rock somehow stayed on his feet.

"Oh, wow! Wow! Will Smith just smacked the **** out of me," Rock said as the audience laughed, thinking it was a skit.

Smith then made what may become one of the most repeated phrases of Oscar history when he shouted, "Keep my wife's name out of your ******g mouth".

Stunned by what had just happened, Rock told Smith it was only a joke, but Smith shouted his phrase a second time, louder and more deliberately.

At that point, many stars in the audience audibly gasped or fell silent. Spectators in the mezzanine stood up and craned their necks to try to catch a glimpse.

Rock struggled to rescue the situation and get the show back on track. "That was the greatest night in the history of television," he said to a smattering of applause and whistles.

The audio from the show, broadcast on a time-delay of a few seconds in the United States, appeared to have been cut from the live transmission for many viewers because of the language. But it was audible in some broadcasts, for example in Japan and Australia.

Jada Pinkett Smith told Billboard in December she has been battling the autoimmune disorder alopecia, which can cause hair loss and balding.

Rock has hosted the Oscars twice, in 2005, when he received mixed reviews, and again in 2016 when, during the #OscarsSoWhite protests, he confronted the Academy over the lack of Black representation.

Smith, 53, has been one of Hollywood's most charming and bankable stars, and was known for his clean rap lyrics when he shot to fame in the 1990s in the television sitcom The Fresh Prince of Bel-Air.

He took on mostly comedy and action roles early in his movie career before expanding into drama. He had twice before been nominated for best actor, for 2001's Ali and the 2006 movie The Pursuit of Happyness.

Smith won this time for playing Richard Williams, the father of tennis stars Venus and Serena Williams.

"Richard Williams was a fierce defender of his family," Smith said, accepting the award through tears in an obvious reference to what had just taken place.

Smith did not mention Rock in his acceptance speech but said: "Art imitates life - I look like the crazy father, just like they said about Richard Williams. But love will make you do crazy things."

Smith, who laced his speech with religious references, also told the audience what fellow nominee Denzel Washington said to him moments earlier: "At your highest moment, be careful, that's when the devil comes for you."

And his final remark before leaving the stage was, "I hope the Academy invites me back."

The Academy did not say whether Smith would be invited back for future shows, but said on Twitter, "The Academy does not condone violence of any form."

In a statement sent to media, and without naming names, Los Angeles police said investigators were aware of the incident, but that, "The individual involved has declined to file a police report."

Should Rock change his mind, however, Smith could be in jeopardy.

"If the involved party desires a police report at a later date, LAPD will be available to complete an investigative report," the statement said.