Chaos erupted at the MGM Grand as a pre-fight press conference ahead of Conor McGregor's UFC 202 rematch with Nate Diaz descended first into farce and then threatened to erupt into a riot.

On another day of 40-degree August heat in the desert, the bitter rivals rained bottles of water down on one another in a quickly abandoned media get-together.

Tensions between McGregor and the UFC had come bubbling back to the surface when The Notorious turned up over a half hour late for the final pre-fight press conference at the casino's David Copperfield Theatre.

(*Warning: contains strong language*)

When he did eventually show, McGregor was mid-way through answering his second question when Diaz stormed off the stage and made for the exits with his entourage.

As they shouted obscenities down at McGregor's camp, the slanging match took a turn for the worse when the camps started to launch water bottles and cans at each other with media caught somewhere in the crossfire and the fans at the back of the arena going wild.

From first viewing it looked as though Diaz may have thrown the first bottle down on the McGregor group himself but they were soon raining in both directions - with McGregor launching a number of bottles from the stage as Dana White pleaded with him to stop.

It wasn't immediately clear if anyone was hurt in the brief exchange but a Las Vegas police officer did confirm that at least one can of an energy drink was thrown.

McGregor was restrained by myriad UFC staff as the organisation's president immediately called a halt to proceedings.

White had begun the press conference in surly form when McGregor's tardiness again clearly irked the sport's figurehead.

This rematch was originally scheduled to have taken place last month at the UFC's summer spectacular but McGregor withdrew - and briefly threatened to retire - over disagreements on media duties.

"He has to start respecting people's time – yours, theirs, David Copperfield's," said White. "We're having a press conference here [with or without him]"

McGregor, coming into this fight on the back of the first defeat of his UFC career, did finally show up around 28 minutes late, immediately insisting he had been incorrectly informed that the conference was to begin at 1.30pm local time, not 1.00pm.

"I thought it was half one, it was half one. Vegas traffic is heavy this time of year. There must be a McGregor show on. These press conferences have helped shape what it is but also they have almost...they have got me kicked off cards."

As he began the answer to the next question, those words proved prophetic. Diaz walked off the stage and chaos ensued.

"F*** your whole team," shouted Diaz as he made his exit behind a row of TV cameras followed by his brother Nick and the rest of his team. "F*** you and the crackhead esses," McGregor roared back. Then came the shower of plastic bottles and cans.

The Diaz crew went out the theatre's front door while McGregor's entourage exited backstage.

Of course, none of this is unlikely to leave White and UFC chiefs overly perturbed in the long run. There could perhaps be some action from the Nevada Athletic Commission in the form of fines.

However, a fight that appeared to be struggling to live up to the same level of expectations as its first instalment has now got all kinds of grist for the hype mill.

McGregor and Diaz are due to be in close confines again on Thursday afternoon with public workouts scheduled in Las Vegas for both fighters. Things are likely to stay interesting.