Watch: Jacinda Ardern on her engagement, the ring and how Clarke proposed

Jacinda Ardern says she has had "absolutely no idea" when her wedding will be.

"We haven't made any plans at all," the Prime Minister told reporters at her post-Cabinet press conference.

Asked about how the proposal by long-time partner Clarke Gayford happened, she said: "There are some things I don't mind keeping for ourselves."

She did say it took place at the top of Mokotahi Hill, and there were also a couple of locals and DPS officers there as well.

She said the ring had belonged to Gayford's grandmother.

She had not been hiding the proposal, but it was sitting on the middle finger because it did not fit on her ring finger.

She said there was also a dog on top of the hill that took a particular interest in the chocolate that Gayford had brought along.

She appeared to indicate that Gayford had not gone down on one knee, saying that the security agents did not notice the proposal.

The couple, who are parents to 10-month-old daughter Neve, became engaged over Easter, a spokesman for Ardern confirmed on Friday.

It is understood the news only emerged because a reporter attending the Pike River ceremony saw the Art Deco style ring on Ardern's left hand and asked Ardern's office about it.

The office later confirmed the news.

It is not known if Ardern or Gayford popped the question but the Prime Minister hinted it would have to be the latter in a previous interview.

Prime Minister Jacinda Ardern has confirmed her engagement to long-time partner Clarke Gayford. Photo / NZME

In a January interview with the BBC Ardern said she would not let Gayford get away with not asking her.

During the interview, Victoria Derbyshire asked Ardern if she would ask Gayford to marry her.

"I would not ask, no. No."

When Derbyshire pointed out she was a feminist, Ardern replied: "Absolutely I'm a feminist. But I want to put him through the pain and torture of having to agonise about that question himself.

"No, that's letting him off the hook. Absolutely not," she said, laughing.