Prime Minister Chris Hipkins and Education Minister Jan Tinetti are making a pre-Budget announcement.

Speaking at Ridgway School in Wellington, Hipkins says he's at the school a year ago to open the new buildings.

He asks the children if they can remember. One tells him the previous buildings were "old and crusty".

"When we became the government ... we had to create space for 100,000 more children in our schools," says Hipkins.

"So far we've found the money to build 2700 new classrooms."

He tells the children the government is releasing its Budget this Thursday, and "we're putting more money into building more new classrooms so that more kids around the country can have the sorts of classrooms like the ones you guys have got".

"We're gonna be building, because of the money that we're putting in, in addition to the money that we've already got, 3000 new classrooms around the country. So that's a lot of new classrooms, this year's Budget funds 300 of those."

He asked who likes the new classrooms.

"Everyone's got their hands up, including some of the teachers, that's pretty cool," he says.

Tinetti addresses the children away from the microphones, and says it's fantastic the kids are in "such wonderful buildings, but we want to see every young person in this country learning in warm, dry, beautiful buildings just like this".

Hipkins says back when Labour came into government in 2017, children were being taught in school gymnasiums and libraries because schools were becoming overcrowded.

The funding from this year's Budget will mean 6600 more student spaces, and he says at the current rate of building the 100,000 extra student spaces needed will have been halved by the end of 2024.

The government has already funded spaces for about another 60,000 students, he says.

"It is an example of where we've invested, over the time that we've been in government, to really bring our schools up to scratch. Of course building new classrooms is only part of the equation - there's also work around building new schools ... and a significant programme to redevelop our existing schools, so we've seen through the Christchurch schools rebuild.

"And for some of our most run-down schools we've been putting a significant focus on big redevelopment projects, so that includes schools like this one where we've been able to completely upgrade their buildings to both cope with population growth but also to cope with the fact that some of the buildings that they were previously dealing with were pretty old and in need of significant replacement work."

Tinetti says 16 new schools have been opened since Labour came into government, and this morning is announcing a further $100m in this year's Budget for up to four new schools.

The new schools will be located "in those role-growth areas, and where the need is for those new schools".

Hipkins says the funding today will maintain the momentum of the government's funding of about 4000 student places every three months.

"That then leaves us with another six years to finish the remaining school buildings that we know will be required."

He says one of the challenging parts of building new classrooms is that's often associated with other work like redevelopment, which can mean it takes a bit longer.

In some cases, relocatable classrooms are used in the short term while the government plans redesign and rebuilds of the school.

"We do occasionally have to make use of relocatable classrooms to make sure that we've got the classrooms there when they're needed, for the growth of the population."

He says schools often do not routinely have air conditioning, but the priority is to avoid having non-teaching spaces like gyms and libraries used as teaching spaces.

Hipkins has signalled a "no-frills Budget" on Thursday focused on "funding the things most important to New Zealanders, like support with the cost of living and cyclone recovery".

-RNZ.