The Government has conceded that some of the sensitive Budget details released today by National are correct.

The National Party claims it has obtained top secret details of Thursday's Budget, including that the Government will spend $1.3 billion in defence.

National have released an "overview of the votes" they say is from this Thursday's Budget.

Votes mean what the Government is allocating to different areas of its overall spend.

Any leak of Budget information ahead of its release day would be a matter of great concern to the Government, as the information is financially sensitive.

Finance Minister Grant Robertson told reporters that some of National's numbers were correct - but others were not.

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

Robertson said the real Budget would be released on Thursday.

He said where the figures came from was being looked into and addressed after Thursday.

They did not come from the Beehive but would not comment on whether they may have come from Treasury.

"Some of the numbers are not correct. You will see on Thursday what those are," Robertson said.

"What I'm saying to everybody is that they should wait till Thursday."

Robertson would not be drawn on which numbers were incorrect and which ones were right.

He said the major new initiatives had not been announced yet.

An investigation into details of how information emerged, and any legal ramifications, would be considered after the Budget.

Robertson said he had been at Labour's caucus when he was told of the release by National and had been looking into it since.

Prime Minister Jacinda Ardern had been interested in how the figures may have been divulged but like him was focused on Thursday's Budget.

Robertson said he had spoken to the Treasury Secretary who was also looking into the issue. He said he had confidence in the Treasury but he would wait to see if that confidence was misplaced.

What National had released was only a fraction of what the Budget contained, Robertson said.

"It's partial information."

Focus on Treasury website

On the Treasury's website, it appears officials have been preparing the information ahead of Thursday's Budget.

Much of the information provided by National, in terms of the estimates of vote funding for 2019 in different areas, was put on the Treasury's website on May 30.

However, when those links are clicked access is denied.

The most likely reason from this, according to the website, was because "the page no longer exists or has moved" and "the page may have been temporary".

Treasury has been approached for comment, as has Finance Minister Grant Robertson's office.

Simon Bridges: 'Loose, incompetent Government'

National leader Simon Bridges is being coy about how National obtained Budget details, declining to describe the matter as a leak.

Asked if this was a cock up, or a conspiracy – meaning was it a deliberate leak or an accident – Bridges would only say it shows a "loose, incompetent Government".

When pressed if the information was leaked, he would not say.

"What we have done with the information we have given you, is put together what we have from the information to protect how and what information we have."

The information includes $1.3b for the purchase of assets in Vote Defence Force in 2019/2020 – this is up $641 million compared to last year, according to Bridges.

"This has nothing to do with the Government's wellbeing priorities. It shows the Prime Minister has yet again had to throw her principles out the window to buy off Winston," Bridges said

Winston Peters, leader of NZ First, is also the Minister of Foreign Affairs.

Fellow NZ First MP Ron Mark is the Minister of Defence.

Peters claims Nats' details 'utterly fake'

Winston Peters told the Herald that every figure used by Bridges was "utterly fake, false, and will be proven so on Thursday".

"His credibility is utterly shot by these sorts of statements.

"He's got them all wrong, you name it and I'll tell you which one's wrong."

Bridges said the spending on defence made a mockery of the Government's inability to settle the teachers' strike and refusal to fund more for dentistry.

"There's money for tanks but not for teachers, there's money for trees but not for teeth."

National said the documents also showed that how much the Government plans to spend on Forestry has doubled - with what will be an extra $139m, for a total of $277m in the first year.

"There will also be $744m for DHBs," Bridges said.

"That will be barely enough to cover business as usual cost pressures including deficits, let alone new initiatives. This clearly won't be enough to cover all of the promises made by the Government."

National released the information just before Labour's weekly caucus meeting.

Robertson was already inside – although he was seen leaving the meeting soon after National released the information.

But Leader of the House, Chris Hipkins, said: "I wouldn't imagine they would have much in the way of details, we certainly haven't given them details".

"The National Party claims a lot of things. I haven't seen any evidence that they have actually got anything."

He said it was a matter for Finance Minister Grant Robertson.

Minister for Children and Internal Affairs Tracey Martin said she had not seen the figures purported to be from Budget 2019 but would recognise them if they were correct.

She said it would be a problem if they were correct Budget figures.

"That would be a problem for the public service, for ministerial services, if that's what's out and about."

Martin called it a "fascinating hypocrisy" for the National Party to be touting what could be a leak when it went to so much trouble to track down the leaker of Bridges' expenses last year.

"They are aiding and abetting something which, if they were in government, they would be freaking out about."

Forestry Minister Shane Jones declined to comment on the Budget figures quoted by National, saying that speaking about them before the leader would mean "certain death".

This is not the first time National has obtained sensitive Government information.

Last month, National were leaked a Cabinet paper on the issue of legalising cannabis from Justice Minister Andrew Little.

It contained four options for a referendum at the 2020 election on the decriminalisation of cannabis for recreational use.

In late December, National revealed to the Herald it had been leaked elements of the Government's Budget Policy Statement ahead of its unveiling later that month.

Speaking to media ahead of his weekly caucus meeting, Bridges said the documents show the Government's priorities are in the wrong areas.

"This Budget may be many things, but it ain't a Wellbeing Budget."

Bridges would not tell media how National got the information – "but I'm very confident in the information".

When pressed on if the information was leaked, he would not say.

"What we've done with the information we have given you, is put together what we have from the information to protect how and what information we have.

"But it is certainly information from the Budget."