NZ election 2020: National Party's Nikki Kaye in tears explaining how breast cancer battle played into decision to quit politics

Outgoing National MP Nikki Kaye has broken down in tears in an emotional interview explaining how her breast cancer battle contributed to her decision to quit politics.

The Auckland Central MP announced she was stepping away from Parliament on Thursday morning, following seismic changes within the National Party that saw her promoted to deputy leader before being demoted again within a matter of weeks.

She told The AM Show on Thursday that the decision was made for personal reasons, and not because the polarising Judith Collins had taken over as party leader 36 hours prior.

But in a moving interview on RNZ's Morning Report, Kaye expanded on the rationale behind her resignation, speaking candidly for the first time about the impacts of a 2016 breast cancer diagnosis which saw her take months off work to receive treatment.

"Being diagnosed with breast cancer - and I have not talked in detail about my health before - I don't see life as a situation whereby you can always plan for things," she said.

"My view is that you have to live every moment, and I have—excuse me," she said, trailing off suddenly after noticing her voice waver, then speaking again through tears.

"I have given everything to this party and the country. I think you have to know when your time is up and you've given it your all."

"I've been through a hell of a lot with breast cancer, and I say to people nothing could be worse than that, so it's not about [the pressures of the past few weeks]."

Kaye says she stepped up to the role of party deputy under Todd Muller's leadership because she felt that was the best way "to make a contribution to New Zealand" at the time - but she now wants to give someone else the opportunity to make their mark.

"There are events outside your control, and from my perspective I've looked at the whole landscape and I feel that now's the time to retire, and it's the best thing."

She told The AM Show she's now looking forward to "a Tuesday night on the couch" and "spending some time on Great Barrier Island".

Kaye's retirement coincided with fellow National MP Amy Adams announcing she would be stepping away from Parliament at the election.

Both are backing new leader Collins, with Kaye describing her as "a real force of nature" who has the capability to guide New Zealand through "the largest economic crisis of a generation" should she win the September election.