ACT Party leader David Seymour accused the government of coming out with a "half-baked, uncosted, bargain-bin" version of ACT's own youth justice policy.
Prime Minister Chris Hipkins on Tuesday said the government would build two new youth justice units catering for up to 30 higher-needs youth. The announcement followed Monday's revealing of new laws concerning youth crime, including making it an aggravating factor in sentencing if someone - youth or adult - encourages someone to offend and post video of their offending online.
"When a young person is sent to a youth justice facility by the court, the public have an expectation that they'll not only be held accountable for the crimes that they've committed, such as a ram-raid, but they'll also receive the rehabilitation support that they need," Hipkins said.
"Youth justice residences need to be secure, safe places and it's become clear that the introduction of 17-year-olds into that system has created challenges and we need to do things differently."
The change to have 17-year-olds dealt with mostly in the youth justice system was first announced by the then National-led government in 2016 and backed by ACT.
Earlier this month ACT said it would revert the change, which had "not delivered on its promises". In May, ACT said it would task Corrections with setting up new youth detention centres, at a cost of half a billion dollars.
On Tuesday, leader David Seymour took aim at the government's intended approach.
"They haven't costed it, they haven't thought it through, they haven't given any detail."
Hipkins rejected the criticism, saying ACT's proposal was more akin to a prison than a rehabilitative facility.
"It's basically a mega-prison for young people. That is not what we're talking about here, we're talking about a continuum of care for troubled young people who have in some cases done serious offending, and who need some serious support."
National said the government was making knee-jerk announcements with the election in mind, rather than any genuine commitment to tackle youth crime.
"They know in 88 days they're going to face the music, because they have been soft on crime for six years," National's justice spokesperson Paul Goldsmith said.
"Changing your tune, doing a massive U-turn three months out from an election, won't wash with New Zealanders."
Green Party co-leader Marama Davidson decried the 'tough on crime' rhetoric coming from the main parties, saying they should be focused on the drivers instead.
She said resources should not be going towards building more facilities, but to community-led projects.
"When the community is resourced to step up in place of youth justice facilities, they are having better outcomes than youth justice facilities. We need to be supporting more of that for the immediate stuff, as well as the long-term drivers of inequity."