David Seymour is accusing Jacinda Ardern of "attempting to rewrite history" over her claim the Government went "hard and early" to stamp out COVID-19.
The Prime Minister announced on Monday that after 17 days of no new COVID-19 diagnoses and no remaining active cases, New Zealand will move to alert level 1 from midnight - meaning all restrictions will lift, except for the border closure.
"Here in New Zealand we went hard and early with a single plan that had a dual purpose - to protect lives and livelihoods," Ardern said, as she congratulated Kiwis for uniting in "unprecedented ways" to "crush the virus".
But ACT leader David Seymour said the Government did not act soon enough, and that despite a call to close the border in February, it "dithered and then had to implement one of the most severe lockdowns in the world".
The Government closed the border to everyone but New Zealanders 20 days after the first case of COVID-19, but Seymour argued it should have happened sooner as we were given "advance warning" as the 60th country to get a case.
"New Zealanders have made significant sacrifices, not least the 37,500 people who have lost their jobs," he said. "We face the real risk of mistaking good luck for good management and making more bad decisions without the good luck."
Seymour criticised the Prime Minister for telling New Zealanders to expect more cases of COVID-19 in the future. He said the Government should have been contemplating how to live in a post-COVID-19 world rather than focusing on achieving "one metric".
Seymour is calling for a Royal Commission of Inquiry into the Government's response, to assess if the border was closed soon enough, and if the Government "appropriately balanced COVID-19 elimination with other goals".
The Prime Minister said she is proud of her Government's response, highlighting how the first economic financial package - which included the wage subsidy scheme - was in place 26 days after the first New Zealand case.
She also defended the strict lockdown measures.
"Had we not acted, 11 days into our lockdown we were projected to have 4000 cases. We had 1000 and one of the lowest rates per capita in the world. That was what the sacrifice of our team of 5 million was for - to keep one another safe, and to keep one another well."
Seymour's response was in stark contrast to National leader Todd Muller, who said he was "delighted" by the Prime Minister's level 1 announcement.
"It's a fantastic day for New Zealand. It's a testament to all our collective efforts over the last many weeks, and I'm sure New Zealanders share my delight that we can now move on to the next phase of this journey which is a significant economic recovery that's in front of us."
Muller said he made it clear last week that he felt the move to level 1 could have happened sooner, pointing to a leaked Government paper that revealed the country was ready for the move.
But Muller said now is the time for "celebration" and that all New Zealanders "deserve a moment of quiet satisfaction that between us all we have managed to achieve this outcome".
Business New Zealand also welcomed the move, with chief executive Kirk Hope saying now is the time to "work together in the same way to manage the economic risks and look after businesses and jobs".