"I want my child to look back on the history books and judge me and this government favourably," the country's pregnant prime minister told parliament on Thursday.

"If we're not here for kids or the future of the country they live in, why are we here? If our budget isn't about people, what is it for? On both accounts, this government is happy to be judged."

After plenty of goodies in December's half-year "mini-budget" and announcements in recent months, the coalition Labour-led government had been playing down the odds of another splurge.

It warned it needed to "rebuild" after what it described as nine years of underfunding of schools and hospitals by the previous centre-right National government.

So it was no surprise Thursday's budget - the first from a Labour-led government in a decade - led with a $NZ3.2 billion ($A2.93bn) boost to health operating funding over four years and $NZ1.6 billion for schools.

Housing was another big winner, with $NZ1 billion to build 6400 state houses over four years among other initiatives.

Of $NZ10 billion of new capital investment promised over four years - to a total $NZ42 billion - $NZ3.8 billion has now been allocated.

Finance Minister Grant Robertson called it a "start".

"We can't make up for nine years of neglect in one budget," he told reporters.

On the fiscal front, New Zealand's government is still looking at budget surpluses out to 2022.

The 2017/18 surplus is tipped to come in at $NZ3.1 billion - $NZ600 million more than expected, largely thanks to a healthier tax take.

And 2018/19 is pegged at an even better $NZ3.7 billion, followed by more, rising to $NZ7.3 billion by 2021/22.

Net crown debt is forecast to drop to 19.1 per cent of gross domestic product by 2022, below the 20 per cent target promised to voters.

But in a fiery speech in parliament, opposition leader Simon Bridges refused to let the government wear the glory, saying its predecessor had "gifted" it an economy to be proud of, which was now being wasted.

"Rebuild what exactly?" Mr Bridges asked.

"Grant Robertson has an enviable position for really any finance minister all around the Western world.

"But for Grant Robertson, enough is never enough."

Meanwhile, Treasury's forecasts for GDP growth has steadied to 3.3 per cent for 2018/19.

It's expected to average 3 per cent in further years while unemployment is expected to flatten out at 4.1 per cent.

But the budget wasn't without what some will call let-downs.

Despite a focus on health, a plan to make visits to doctors cheaper has become more narrowly targeted. Promised funding for 1800 new police officers has largely been pushed out to 2020.

Ministers have warned deals with its allies in government, combined with a promise of no new taxes or borrowing, have meant some tough decisions for Labour.

Australian Associated Press