Finance Minister Grant Robertson said the Budget priorities would be properly released on Thursday.

The priorities for the Government's "wellbeing budget" in 2019 have been leaked.

The five priorities identified in the snippet of text leaked to the National Party and then released to media include a focus on mental wellbeing, reducing child poverty and family violence, lifting Maori and Pacific incomes, digitising the nation, and transitioning to a sustainable and low-emissions economy.

Above this list of five priorities is a requirement that all portfolio ministers identify at least one per cent of the "lowest priority" expenditure in each portfolio's baseline, presumably to be re-prioritised.

"Each portfolio minister will be required to undertake a review within their portfolio(s) to identify at least one per cent of expenditure, within each portfolio's baseline that is not in line with the Government's objectives, or is the lowest priority," the excerpt provided by the National Party reads.

The Government undertook a reprioritisation of spending before the last budget too and it is understood this is fairly routine.

The focus on "supporting the mental wellbeing for all New Zealanders" includes a "special focus on under 24s".

The priorities are due to publicly unveiled as part of the Budget Policy Statement on Thursday at the Half-Year Economic and Fiscal Update.

Finance Minister Grant Robertson said reprioritisation of spending was an ongoing and already-public process and further details would be available on Thursday, but his office did not dispute any of the priorities listed.

ROSS GIBLIN/STUFF Amy Adams: "I think what it shows is that the Government finances are incredibly tight and makes a mockery of this Government saying many areas are underfunded."

"As I said in the House last week, reprioritisation is an ongoing process. To respect the confidentiality of the Budget process, I am not going to comment on any specifics for Budget 2019 as the Budget process is underway," Robertson said.

"Budget priorities will be announced as part of the Budget Policy Statement on Thursday."

National's finance spokeswoman Amy Adams said the priority areas were "high level and reasonably generic" and didn't give much detail of the Government's supposed "transformative" change priorities.

"This supports my view that the Wellbeing Budget, other than the branding and the platitudes, is not going to be terribly different from what New Zealanders have seen in previous years," Adams said.

Ministers are currently preparing their budget bids and its understood the five priority areas are intended to be used as a kind of "lens" for every bid - each minister should consider how their priorities match with them.

Adams also lashed out at the reprioritisation goal.

"I think what it shows is that the Government finances are incredibly tight and makes a mockery of this Government saying many areas are underfunded when the first thing they want to do is find ways to cut expenditure."

The snippet of text was released to Stuff as a photo of a printed page of text. It is not known how this document found its way into the hands of the Opposition.