The head of the Treasury says a review will investigate how the National Party obtained Budget information ahead of its release.

Secretary to the Treasury Gabriel Makhlouf said the release of Budget 2019 would still proceed as planned this Thursday.

This follows the National Party this morning releasing information that they say will be in Thursday's Budget.

Speaking to media this morning, Finance Minister Grant Robertson confirmed that some of the numbers released by National were correct, but some of them were wrong.

Robertson said he "was just not going to get into" how much of the information was accurate.

National said the figures were from Budget 2019, but Robertson said what had been released was not Budget 2019.

But he is confident the numbers did not come from the Beehive and, like Prime Minister Jacinda Ardern did this morning, said any leak did not come from Cabinet.

"I want to be absolutely clear; this material has not been leaked from the Beehive."

This is because, he said, the numbers released by National were not put together in a way that had been received in the Beehive.

However, National Leader Simon Bridges said this morning that the information had been "put together what we have from the information to protect how and what information we have".

Robertson said he had confidence in the Treasury - but warned that could change, depending on the outcome of an investigation.

"This is something we will investigate to see whether or not that confidence is maintained."

Secretary to the Treasury Gabriel Makhlouf said the release of Budget 2019 would still proceed as planned this Thursday.

Robertson said he spoke to Makhlouf this morning.

He said the Treasury was now looking to find out what has happened.

"The investigation, or looking into it, is a matter for me for after the Budget."

Asked if he thought it was more likely to be a leak, than an accident, Robertson said he didn't know at this stage and that's "not something I'm focused on at this stage".

He said the information was "not even a fraction of what the real Budget is".

But when asked if it was embarrassing for the Government, he said: "No, not particularly because this is not the real Budget".

"The real Budget is about the big priorities we've got around taking mental health seriously, reducing child poverty, working on improving the economic and social opportunities for Maori and Pasifika."

Robertson said after the Budget was released the Government would look into the issue.

He said he works with the Treasury and said there would be "work done to work out what happened here".