New Zealand half-back Aaron Smith has been suspended for one game after allegedly having sex in an airport toilet last month.

The 27-year-old was seen entering a disabled toilet at Christchurch Airport with a young woman on Sunday, September 18, the day after the All Blacks' victory over South Africa.

"The pair were in the bathroom for 5-10 minutes and from the noises coming out of the bathroom there was absolutely no question what the couple were doing in there," a witness told the NZ Herald. "Mr Smith then came out of the room on his own straightening up his white checked shirt and black dress pants.

"About a minute later the young lady comes out of the same toilet cubicle looking equally suspicious. I myself did not have a problem with this... my wife however is protesting that this is disgusting for a public figure to do this.

"He essentially occupied a public cubicle reserved for the disabled for up to 10 minutes. This was not discreet, it was 2pm on a Sunday where there were a lot of children and fans around. He was in his full All Blacks uniform and there was not an ounce of remorse or regret on his face. He buttoned up his shirt and sat back down with his team mates and carried on smiling chatting like nothing had happened."

All Blacks coach Steve Hansen said: "I had a conversation with Aaron who confirmed the story. As a result of this the leadership group met and were unanimous in the fact the behaviour wasn't acceptable and as a consequence a one match suspension would be put in place.

"Clearly Aaron is bitterly disappointed in his behaviour and feels he has let the team down but just as importantly he feels bitterly disappointed in letting his family and his partner down.

"At his request has asked to go home to deal with the personal matters that have come with this incident and we are happy to support him with that."

The suspension means that Smith will now miss the Rugby Championship match against South Africa in Durban on Sunday.