New Zealand's Prime Minister Jacinda Ardern was worried she may have caused a "diplomatic incident" after reportedly claiming that Donald Trump mistook her for Justin Trudeau's wife.

Canadian leader Trudeau was supposedly making the introductions as Ardern attended her first major forum since taking office last month when Trump mixed-up the 37-year-old with the Canadian leader's partner Sophie.

At the time, it was reported that it took the President several minutes to realise his mistake.

However, Ardern said she regretted the gossip getting out and played down the story after reporters seized on it.

She said she didn't want to "cause a diplomatic incident" and claimed some details were mangled in the retelling.

She said "a third party" at the meeting of world leaders - who she refused to name - incorrectly thought Trump had failed to identify her and she later told the anecdote to friends back in New Zealand.