Jon Jones sent Stipe Miocic into retirement with a stunning back kick to the ribs and used a series of blows to the head in the third round to retain the UFC heavyweight championship in front of US president-elect Donald Trump in the main event of UFC 309 at Madison Square Garden on Sunday afternoon AEDT.

Jones posed and played to the crowd on top of the octagon in front of Trump, Elon Musk, picked by Trump to lead a new Department of Government Efficiency, and Robert Kennedy Jr, Trump's choice to lead the Department of Health and Human Services in his incoming administration.

Trump walked out to a rousing ovation in front of 20,200 fans just before the start of the pay-per-view card and seemed to bask in thrill of the fighters that throughout the night gave him props — including Jones.

"I want to give a big, big thank you to president Donald Trump being here tonight," Jones said to a roaring ovation that bled into a "USA! USA!" chant.

"I'm proud to be a great American champion," Jones said.

Widely considered the best fighter in the world, Jones (28-1-0; 1 NC) was the aggressor from the start and landed a series of shots to Miocic's head in the first round. Jones showed he has plenty of fight left in the tank.

British heavyweight Tom Aspinall looms as the next challenger for Jones. Aspinall won a fight for the interim heavyweight title last November in the Garden. UFC CEO Dana White had promised Aspinall, who chatted with Arizona Cardinals QB Kyler Murray, would challenge the winner of the main event in a unification bout.

"As far as my future in the octagon, I decided that maybe I will not retire," Jones said. "I know that we have options.

Miocic (20-5) failed in his bid to win the heavyweight crown for a third time and immediately announced his retirement.

"I'm done," Miocic said. "I'm hanging 'em up."

White captioned a photo he posted on social media "the boys", which featured him with Trump, Kid Rock and Musk. 

Trump pumped a fist during an occasional outbreak of "USA! USA!" chants. He was flanked on his front-row seat by White on his right and Musk on his left and politely applauded the fight winners.

UFC fans wore red Trump hats and some waved flags emblazoned with his image during breaks in the action.

AP