• Referring to Pinkett Smith's shaved hairdo, Rock said: "Jada, can't wait for GI Jane 2."
• Smith walked up on stage and appeared to strike Rock before returning to his seat and shouting: "Keep my wife's name out of your... mouth."
Will Smith hit Chris Rock in the face on stage at the Oscars after the comic made a joke about the actor's wife Jada Pinkett Smith.
Referring to Pinkett Smith's shaved hairdo, Rock said: "Jada, can't wait for GI Jane 2."
Smith walked up on stage and appeared to strike Rock before returning to his seat and shouting: "Keep my wife's name out of your... mouth."
Smith later apologised in a tearful best actor acceptance speech.
"I want to apologise to the Academy. I want to apologise to my all my fellow nominees," Smith said after winning the first Oscar of his career for playing the father of tennis legends Venus and Serena Williams in King Richard.
"Art imitates life. I look like the crazy father, just like they said about Richard Williams. But love will make you do crazy things."
Pinkett Smith has previously spoken about having the hair loss condition alopecia.
Rock looked shocked in the immediate aftermath of the incident, telling the audience: "That was the greatest night in the history of television."
He then handed over the best documentary prize, which was the reason he was on stage.
His joke referred to 1997 film GI Jane, in which Demi Moore played the title role with a buzzcut.
Backstage shock
By Steven McIntosh, entertainment reporter at the Oscars
Backstage here in the Dolby Theatre in Los Angeles, there was a shocked reaction from journalists to Smith's run-in with Rock.
Reporters had been taking part in a press conference where the winners appear after delivering their acceptance speeches.
But attention suddenly turned to our overhead screens and what was going on at the ceremony, as it became clear something serious was kicking off.
At first, it had seemed like a joke or some kind of set-up. Smith even appeared to laugh at first after Rock delivered his joke about his wife looking like G.I. Jane.
Jada looked annoyed, but at this point it was assumed this was all part of some kind of pre-planned joke.
Doubt began to creep in when Smith rose from his seat and hit Rock on the stage.
Of course, both these guys are veterans of film and television, and would know how to carry out a fake stage slap. Except, everyone was starting to think, it didn't look that fake.
By the time Smith was sitting back in his seat and shouting to Rock to "keep my wife's name out your [expletive] mouth," it was clear this was no sketch. A professional like Smith would know better than to drop the F-bomb on stage during a live TV broadcast.
Viewers at home didn't hear the swearing, of course. Broadcast network ABC had cut the live feed to avoid offending viewers at home.
There was silence in the winners' room. Academy staffers looked just as shocked as the journalists did. "I thought they were doing a bit," one said to his colleague.
Rock, meanwhile, looked visibly shaken. But, realising he'd just made Oscars history, he made light of the situation, commenting: "That was the greatest night in the history of television."
Much like previous Oscars which were defined by their viral moments - such as Ellen's group selfie or the best picture winner mix-up in 2017 - this will now forever be the Oscars where Will Smith punched Chris Rock.
Pinkett Smith first talked about her hair loss struggle in an episode of her Facebook chat show, Red Table Talk, back in 2018.
She said: "I've been having issues with hair loss. And it was terrifying when it first started."
The Girls Trip star said she first suspected she had alopecia after "handfuls of hair" came loose in the shower.
"I was just like, 'Oh my God, am I going bald?' It was one of those times in my life where I was literally shaking with fear," she explained. "That's why I cut my hair and continue to cut it."
According to The Hollywood Reporter's Scott Feinberg, after the incident a tearful Smith needed to be "pulled aside and comforted" by Denzel Washington and Tyler Perry during an advert break.
"Will and Chris, we're going to solve that like family. Right now we're moving on with love," said Sean "Diddy" Combs, presenting the next section.
Other winners at Sunday's ceremony included Jessica Chastain, who picked up best actress for The Eyes of Tammy Faye; Jane Campion, who won best director for The Power of the Dog; and Apple TV film Coda, which was named best picture.
Best supporting actress went to Ariana DeBose for West Side Story, while Troy Kotsur won best supporting actor for Coda, which also picked up best adapted screenplay.
Sci-fi epic Dune won six awards in total including technical categories including best visual effects and best cinematography.
Will Smith's best actor acceptance speech in full:
Richard Williams was a fierce defender of his family. In this time in my life, in this moment, I am overwhelmed by what God is calling on me to do and be in this world. Making this film, I got to protect Aunjanue Ellis, who is one of the most strongest, most delicate people I've ever met. I got to protect Saniyya [Sidney] and Demi [Singleton], the two actresses who played Venus and Serena.
I'm being called on in my life to love people and to protect people and to be a river to my people. I know, to do what we do, you've got to be able to take abuse. You got to be able to have people talk crazy about you. In this business, you've got to be able to have people disrespecting you, and you've got to smile, you've got to pretend like that's OK. What I loved was, Denzel [Washington] said to me a few moments ago, he said, 'At your highest moment, be careful, that's when the devil comes for you.'
I want to be a vessel for love. I want to say thank you to Venus and Serena and the entire Williams family for entrusting me with your story. That's what I want to do. I want to be an ambassador of that kind of love and care and concern.
I want to apologise to the Academy. I want to apologise to all my fellow nominees. This is a beautiful moment and I'm not crying for winning an award. It's not about winning an award for me. It's about being able to shine a light on all of the people - Tim [White, producer] and Trevor [White, producer] and Zach [Baylin, writer] and Saniyya and Demi and Aunjanue and the entire cast and crew of King Richard, and Venus and Serena, the entire Williams family.
Art imitates life. I look like the crazy father, just like they said about Richard Williams. But love will make you do crazy things.
And my mother… a lot in this moment is really complicated for me but to my mother, she didn't want to come out. She's had her knitting crew who she's in Philly watching with. Being able to love and care for my mother, my family, my wife… I'm taking up too much time… Thank you for this honour. Thank you for this moment and thank you on behalf of Richard and Oracene and the entire Williams family. Thank you. I hope the Academy invites me back. Thank you.