People can now get their booster vaccinations three months after their second shot rather than wait for four months as the Government tries to stay ahead of Omicron.
Covid-19 Minister Chris Hipkins said the three-month interval would apply from Friday.
It would mean one million more New Zealanders aged over 18 would be eligible.
It followed advice from the director general of health and the Covid-19 Vaccine Technical Advisory Group.
Several other countries have made a similar move as they deal with Omicron, and experts here have also called for a smaller gap to try to avoid a large peak.
"This is a significant step in our response to the Covid-19 pandemic as it now means a total of 3,063,823 people aged 18 and over – two thirds of our population – will be eligible for their booster from this weekend. Over 1.3 million people have already got theirs," Hipkins said.
"I urge every New Zealander who is eligible for a booster to get it as soon as possible. We are in a race against Omicron and the more people who are boosted the more we can reduce the impact of the outbreak."
He said bringing forward the timing would help those who were immunised more recently - especially among Maori for whom the uptake of the initial vaccine doses was slower.
"Boosters lower your chances of getting very sick from the Omicron variant of Covid-19 and ending up in hospital. Fewer hospitalisations from Covid-19 will mean our health system can continue to provide the full range of care people need, in particular for our most vulnerable such as people with disabilities or long-term illnesses."
The announcement comes ahead of the Prime Minister's speech tomorrow, in which she will set out the dates on which the international borders will reopen to returning New Zealanders.
The Government is trying to slow the spread of Omicron to buy more time to get people boosted.
About 94 per cent of New Zealanders aged over 12 were now fully vaccinated, and about a quarter have had a booster shot, Hipkins said.
"Now is our opportunity to build on that. We have given ourselves a head start that we cannot afford to give up."
Hipkins said there was enough supply in the country to cope with the boosters.
The shorter interval only applies to those who had the Pfizer vaccine, which is most people. Advice on boosters for those who had the altenative Astra Zeneca injection would come later this month.
People aged over 18 can check when they are due for a booster by visiting mycovidrecord.nz or calling the Covid Vaccination Healthline 0800 28 29 26 (8am-8pm, 7 days a week).