Simon Bridges is staying tight-lipped on whether the National Party was involved in Jami-Lee Ross being sent to a mental health facility over the weekend.
"I'm not going to comment on the details, and I'll tell you why: I only learnt about it after the event," Mr Bridges told The AM Show on Wednesday.
"I have some second hand accounts of what has happened, but the reality is I don't know for sure, so I'm not going to engage in that."
Police arrived at Mr Ross's home early on Sunday morning and he was taken to a mental health unit. It's understood he did not go voluntarily and questions have been raised over whether the National Party was involved in his sectioning.
National Party President Peter Goodfellow also would not answer questions over the party's involvement, telling Interest.co.nz he would not "go into detail of it".
Mr Goodfellow also said he would "let them answer", referring to National MPs, when pressed on whether any National MPs were involved.
"This is a matter to do with one of the MPs though, and given those circumstances, I'll just leave it for somebody else to answer that question," Mr Goodfellow told interest.co.nz.
But Mr Bridges would not go into further detail, and appeared frustrated by the suggestion of National's involvement in Ross's sectioning. He told The AM Show: "If you're saying the National Party do this, I reject that with every fibre of my being."
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He said police and health authorities would "deal with these things, not National", adding, "I only learnt about [Ross's sectioning] after the event".
Mr Ross has had made headlines due to his claims the National Party had broken donation laws, as well as allegations he had harassed women in the party, and suggestions he leaked Simon Bridges expenses.
Both National and its leader have taken a hit following the scandal involving Mr Ross. The latest 1NEWS Colmar Brunton poll shows Labour is now ahead of National in the eyes of the public. Mr Bridges' ranking as preferred Prime Minister has dropped significantly.
But he seems confident the scandal will not affect his leadership, telling The AM Show it has been one of the "toughest weeks for National and I think for any leader in living memory".
"I feel personally, I have come through this stronger, and I wasn't to assure the voters I know what we've got to do, and this is to hold this Government to account on a myriad of things they are getting wrong."
Watch the full interview with Simon Bridges above.
The AM Show with Duncan Garner, Amanda Gillies and Mark Richardson, weekdays 6-9am on RadioLIVE and streaming live to the rova app on Android and iPhone.