Morgan was watching the Oscars at home on TV and tweeted: "It was real. Just seen the uncensored footage. Will Smith hit Chris Rock for cracking a GI Jane joke about his wife Jada Pinkett Smith (who suffers from alopecia) - then twice screamed 'keep my wife's name out of your f***ing mouth' at him.
"Ugliest moment in Oscars history."
He added: "Astonishing", and "INSANE."
He then shared a picture of himself playing the piano to the Fresh Prince of Bel-Air star captioned: "That time I played Let It Be to Will Smith… #WhenIFindMyselfInTimesOfTrouble "
— Piers Morgan (@piersmorgan) March 28, 2022
Reid said: "I would just like to make it clear, I do not think it is okay, unless somebody is in physical danger and you need to protect them, or you need to save them in some way by physically intervening, I don't think it's okay to slap anybody."
She added: "I'm not saying it's wrong just because it's my job to argue against things."
Ranvir Singh said: "I agree with Susanna that it's not okay. But the red mist came down, and that's a very human condition."
One Direction's Liam Payne, who was in the audience, told GMB: "I believe whatever he felt he did that he did, he had the right. I also felt there were three losers in one fight. He didn't know – being Chris Rock. He didn't want to do what he had to do – being Will Smith. And she did nothing – being Jada.
'I believe whatever he felt that he did, he had the right to do.'
'I had to leave my chair I'll be honest with you, it cut me really deep.'@LiamPayne reacts to the dramatic moment Will Smith hit comedian Chris Rock on stage at the Oscars for making a joke about his wife. pic.twitter.com/OGT4bA8jDi
— Good Morning Britain (@GMB) March 28, 2022
"But it was a powerful moment for me to sit and watch one of the world's best emoters speak from the heart, and I would rather take the beauty out of the situation than the pain.
"But I had to leave my chair, I'll be honest with you, it cut me really deep. I'm sure everyone's very apologetic about the situation, but ask yourself what would you do in the same situation? We're all very human, right?"
The Academy said in a statement that it does "not condone violence of any form".
Rock, 57, who was on stage to present the award for Best Documentary Feature, made a comment about Pinkett Smith possibly starring in a sequel to G.I. Jane due to her bald head.
Pinkett Smith, 50, has spoken openly in recent years about losing her hair due to alopecia and seemed to roll her eyes in reaction to the gag.
Smith, 53, then approached Rock on stage and hit him in the face, shocking the comedian before returning to his seat.
Viewers in the UK and other countries then heard Smith yell at Rock several times to, "Keep my wife's name out of your f***ing mouth", while the US broadcaster cut the audio.
The Los Angeles Police Department has said it is not currently investigating the incident.
Smith went on to take to the stage after being named Best Actor for his performance as Richard Williams — the father of tennis champs Venus and Serena Williams — in King Richard.
Watch: Celebrities react to Will Smith's Oscars slap