Richie Mo'unga has apologised and vowed to be a better role model after Crusaders players were slammed for an "unacceptable" breach of coronavirus lockdown regulations.

All Blacks fly-half Mo'unga headed to Malvern Park in Christchurch on Monday to train on his own, but arrived when another two groups of his team-mates were also training.

Malvern Park said he adhered to government rules by keeping his distance, but was filmed throwing a ball to one of his colleagues.

New Zealand prime minister Jacinda Ardern was critical of the quintet, which also included Sione Havili, Isi Tu'ungafasi, George Bower and Andrew Makalio, and New Zealand Rugby Chief executive Mark Robinson said their actions were "unacceptable."

Playmaker Mo'unga said he was acting on instinct by picking up the ball, but said he had not arranged to meet his team-mates - with the other two bubbles permitted to head out with each other as they live together.

He said in a video posted on Instagram: "I want to start by saying this was not an organised training. There were no communications beforehand or the night before to say we should train together.

"It was by coincidence that I rocked up and they were there training, just finishing up their session. My local park is their local park, our training schedules were the same, so we run on the same days and it just happened to be it was the same time.

"As I arrived, I yelled to the boys from afar asking how they were and went about my running session.  As I'd finished one of my running sessions, the ball had been kicked over and instinctively I went and picked the ball up and threw it back to them.

"I will say that was the only interaction I had with them apart from talking to them. It's something that was so instinctive for me to do, to pick the ball up and throw it back to them.

"I didn't think twice about it, it's something that happened fast. It's something that I've learnt that even my natural instincts I need to be more careful of and will be more careful of. 

"It doesn't excuse the fact that there were two other bubbles that were passing the ball around together and it doesn't excuse the fact that I can be a better role model in telling the boys 'look, you guys are done, you guys should head home now'. I am sorry for that.

Colin Mansbridge, chief executive of Super Rugby champions the Crusaders, said he is confident "there wasn't a conscious effort to flout the rules" but lessons must be learned.