Listen: Jacinda Ardern talks to Newstalk ZB's Hosking

Prime Minister Jacinda Ardern will spend Auckland Anniversary Day at a maritime commemoration and a music festival.

Auckland is commemorating its maritime and trading history with one of the world's biggest one-day sailing regattas today.

It's just one of the events on Auckland Anniversary Day on Monday. Ardern is attending, and speaking at, the Laneway Festival in Albert Park about 11.30am.

• Listen live: Jacinda Ardern speaks to Mike Hosking

Meanwhile Ardern's partner, Clarke Gayford, has spoken to a British newspaper about being New Zealand's "first man".

He said he's always been attracted to ambitious women but reckons he's "hit the jackpot" with Ardern.

He also says the rush of thoughts through his mind when told by Ardern she was pregnant was the question: "How on earth is she going to cope given everything else that is on her plate at the moment?"

But Gayford, 40, told Britain's Sunday Times watching his partner handle coalition negotiations left him in no doubt they could achieve anything together.

"The one thing that stood out for me through all of the white-hot heat of the negotiations – and there was a huge amount of pressure going around back and forth – she was the calmest I have ever seen," he told the Sunday Times.

"She just rolled through the middle of it so unbelievably well. She just stepped up into that environment. It was stressful, obviously, but I never saw it become too much at any point.

"And I drew from that for strength and thought, 'if we can get through that, we can get through anything'.

"Anyone who knows me knows I've always been attracted to ambitious women and I think I've probably hit the jackpot."

Prime Minister Jacinda Ardern and partner Clarke Gayford at home in Pt Chevalier, Auckland. Photo/Doug Sherring

Ardern, 37, broke the pregnancy news to Gayford by video call when she was in Wellington and he was filming another episode of his TV show, Fish of the Day.

"You get to learn your partner well, don't you? And as soon as something is slightly amiss, you become very keenly aware something is different and you want to know what it is," he said.

"You get that flush of adrenalin like you're about to get some really bad news."

Gayford said the bombshell she was pregnant was an absolute surprise. The couple had previously sought help from fertility specialists but stepped back from doing so when she was made Labour leader.

He said they had treasured their secret in the months leading up to the announcement.

"There were a few people we had to let know over time. Every time it felt like we were giving up a little bit of our secret.

"And because she had become such public property, you hang on to those little things."

Gayford also told the Sunday Times about the huge change to their relationship since she became Prime Minister.

"I used to be able to pick up the phone and call her whenever I liked. I can still do that but the chance of her answering … has diminished rapidly."

Gayford told the British paper they had escaped to Australia for a week of relative anonymity.

But the visit saw the couple met by an official limo and diplomatic detail which delivered them to their first destination - a budget car rental office to pick up one of its lowest cost vehicles.

Prime Minister Jacinda Ardern with her partner Clarke Gayford, on the day after last year's election. Photo/Brett Phibbs

Baby plans he shared included the couple looking at forming a dads' group to meet at Premier House, the official residence of the Prime Minister in Wellington.

There was also work being done by her office to find a place "where I can do a nappy change and not disturb Cabinet members coming through".

He told the Sunday Times there might even be a nappy change on the Prime Minister's desk: "I probably should do that, just to say it has been done."