UPDATED 5.38PM National MP Nikki Kaye has been diagnosed with breast cancer and will be stepping down from her Ministerial portfolios as she receives treatment.

The 36-year-old has posted on Facebook that she received the "devastating news" on Friday.

She says having the opportunity to serve as the MP for Auckland Central and hold the role of Cabinet Minister is a huge privilege, and the Prime Minister has appointed acting Ministers to cover her portfolios.

Ms Kaye says she is fortunate to have hardworking staff and National Party colleagues who are helping ensure support is there for her constituents.

She's asked for space and privacy while she undergoes immediate treatment.

The Prime Minister's offering her his, and his colleague's full support.

"I've spoken with her and assured her that she has the full support of her colleagues and I as she deals with this difficult diagnosis. Her medical team is working hard to ensure a full recovery. I wish Nikki all the very, very best.

"Nikki's young, she's very fit and she's extremely determined and she's a fighter so I'm sure she is going to get through this and will be back with us. She is likely to be away for a period of time measured more likely in the months rather than the weeks, I would have thought."

Gerry Brownlee will act as Minister of Civil Defence, Nathan Guy as Minister for ACC, while Anne Tolley will step into Youth portfolio and Hekia Parata will take on Ms Kaye's Associate Education responsibilities.

MPs expressed shock and sympathy on social media today in response to Kaye’s decision to stand down.

Justice Minister Amy Adams posted on Twitter: “Nikki has our full support and we're looking forward to welcoming her back soon.”

Labour MP Jacinda Ardern, who is Kaye’s rival for the Auckland Central seat, tweeted: “This is gutting news Nikki. Thinking of you and wishing you the speediest recovery.”

Cabinet minister Steven Joyce said: “Get well, Nikko. We’re all thinking of you.”

United Future leader Peter Dunne said: “Terrible news re @nikkikaye. Best wishes to her for a full and speedy recovery.”

@nikkikaye This is gutting news Nikki. Thinking of you and wishing you the speediest recovery.

— Jacinda Ardern (@jacindaardern) September 5, 2016

Nikki has our full support and we're looking forward to welcoming her back soon https://t.co/hsBP2TcwYu

— Amy Adams (@amyadamsMP) September 5, 2016

Terrible news re @nikkikaye. Best wishes to her for a full and speedy recovery

— Peter Dunne (@PeterDunneMP) September 5, 2016

Labour leader Andrew Little said he hoped Kaye made a swift recovery.

“Health is pretty crucial. You only get one chance in life, so we wish her well for addressing her health issue.

Little said Kaye was a “hard-working, reasonably new minister”.

“But it doesn’t matter who it is. You get a big health scare, you’ve got to be able to have the time to go and deal with it.

“It’s the right thing and it’s important that she is given the opportunity to get back on her feet.”

Green Party co-leader James Shaw said the cancer diagnosis was “a real personal tragedy for Nikki Kaye and for her family”.

“I just want to wish her all the best of luck and the best for her recovery… and I hope that she gets all the support she needs.”

Ms Kaye entered Parliament in 2008 as the National Party's first-ever Auckland Central MP, claiming an electorate which had been held by left-leaning parties for 90 years.

She held onto the electorate by very narrow margins against another rising star, Labour's Jacinda Ardern, in 2011 and 2014.

Ms Kaye became a government minister in 2013, taking on the Food Safety, Civil Defence and Youth Affairs portfolios, and associate education and immigration roles.

After re-election in 2014, she was given greater responsibility, taking on the ACC portfolio.

She is part of National's socially liberal wing. She worked on a cross-party group to legalise same-sex marriage in 2013, and led a campaign within her party to keep the alcohol purchase age at 18 years old in 2012.

Ms Kaye was born and raised in Auckland, growing up in Epsom and Kohimarama.

Her parents separated when she was seven, and she was one of nine siblings or half-siblings.

She was head girl at Corran School (now part of St Kentigerns) and studied genetics and law in Dunedin and Auckland.

She joined the National Party in 1998 and began working for then-Leader of the Opposition Bill English in 2002. After a stint in policy work in the United Kingdom, she returned to New Zealand in 2007 to run for Auckland Central.

Ms Kaye is also a keen runner, and won the Auckland Women's 3000m event in 1997.