The Prime Minister and leader of the Opposition engaged in a tense exchange today during Question Time, around priorities from the Budget.

"Why did her Budget take $100 million out of mental health and only put $10 million back in?" Simon Bridges asked.

Jacinda Ardern said the $100m "was not actually allocated to any specific project, it was a list of pilots, some of which didn’t happen".

"What we have funded is a project to enable under-25s to access free mental health care, we've extended nurses in schools for young people to decile four, we've already funded mental health support in Canterbury and Kaikoura, and amongst the $750m in capital for health, it includes upgrade for mental health facilities," she said.

Mr Bridges asked why the boost of almost $1 billion into foreign affairs and aid was "more important" than $100m into mental health.

"I'm surprised that Member no longer supports New Zealand upholding its international obligations, and I take this as now being on record that under National there would be a cut in overseas aid and development,” Ms Ardern said to Mr Bridges.