The government is to reveal its plans for Waikeria prison this afternoon and it's being told it must build a bigger jail, or risk public safety.
The National Party says the government's refusal to build a 3000-bed mega-prison at Waikeria, coupled with its "softer" approach on crime, will ultimately result in more dangerous offenders on the loose in the community.
Party leader Simon Bridges said there were multiple reasons why a bigger prison at the Waikato prison site made sense.
"The prison is required, not just because of the increase in prison muster, but actually because this is a 1911 building that requires significant works - not a half pie job - to ensure the prisoners and prison officers are safe.
"My question to the prime minister is really clear: is it the rebuild of this prison, or is it more victims on our streets and less safe communities around New Zealand?"
A report by the Corrections Inspectorate last year found buildings at Waikeria are in poor condition.
It highlighted issues including overcrowding, at-risk prisoners being kept in their cells 22 hours a day, and an increase in double-bunking - including in units where that practice was never envisaged as possible.
And prisoner numbers continue to climb, with Corrections putting the prison muster at nearly 11,000. As of last month there were just 400 spare prison beds.
Corrections Minister Kelvin Davis said the government was on track with its promised offender-reduction goals.
"There's a whole suite of things we are considering to reduce the prison population by 30 percent over 15 years - but it is going to take 15 years," he said.
Nearly $200 million out of this year's Budget is going to build 600 temporary prison beds, but Prime Minister Jacinda Ardern has refused to follow through with the previous government's Waikeria prison proposal.
"As a government we do not believe in building US-style mega-prisons. It's not the New Zealand way, and doesn't make us necessarily any safer," she said.
"However it is clear that Waikeria has some significant infrastructure issues that we've inherited - and so that's what we have to address."
Mr Davis will reveal the government's plans for the site at an announcement at Waikeria prison at 4pm.