Jacinda Ardern takes a break from campaigning for sister's wedding

Jacinda Ardern's admitted she almost skipped her sister's wedding because she's been so focused on the election campaign.

But as her sister's big day got closer, the Labour deputy realised it was more important than her own - so got on a plane at the last minute. 

Ms Ardern posted a video of the surprise on Facebook, which shows her sneaking down a courtyard into a garden, where she astonishes her sister, the pair dissolving into laughter and tears.

Ms Ardern wrote that when her only sister, who lives in London, told her several months ago that she was getting married, "I just couldn't see how I could get there. The election was so close and there were already so many commitments."

"As her big day got closer, I knew I'd made a massive mistake. I remember telling Andrew [Little, Labour leader] and he totally agreed 'you have to go'. So, without telling my sister I booked a flight and arrived the day before her wedding to surprise her."

Thanking her colleagues for covering her while away, she said she felt "so lucky and privileged" to be able to walk her sister down the aisle.

The election is on September 23.