Government minister Nikki Kaye is on leave after being diagnosed with breast cancer.
The 36-year-old Auckland Central MP issued a statement saying the news was devastating for her and her family.
On her Facebook page, Ms Kaye said she informed Prime Minister John Key on Friday and would be taking leave of absence from her ministerial roles.
"I feel so lucky to have such an amazing family and group of friends who are giving me buckets of love and have been so strong helping me work through this," she wrote.
"I also want to acknowledge the PM who has been hugely caring and supportive."
Ms Kaye also requested a "bit of space and privacy" as she gets treatment and focuses on getting well.
Mr Key said he had spoken with Ms Kaye and assured her she has the full support of her colleagues as she deals with the difficult diagnosis.
She would begin treatment shortly, following the diagnosis last week.
"Her medical team is working hard to ensure a full recovery," said Mr Key. "Nikki will be dedicating her energy towards getting well, and I wish her all the best."
Mr Key said Ms Kaye's Youth, Civil Defence and ACC portfolios would be reallocated in the meantime.
Gerry Brownlee will take over Civil Defence and Nathan Guy will act as Minister for ACC.
Anne Tolley will act as Minister for Youth and Ms Kaye's Associate Education responsibilities will be taken over by Hekia Parata.
Ms Kaye has been the National MP for Auckland Central since 2008.