"Don't put it off, please take the opportunity now," Ardern said.
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.
Ardern said the change to a three-month gap would mean an extra 100,000 Māori would be able to get their boosters.
Ardern said it would mean 76 per cent of New Zealanders who were fully vaccinated would be eligible for a booster from Friday.
"Although Omicron is for many people a mild illness, it can be serious for some and can overwhelm hospitals." She said high numbers of cases, would put the hospital system under serious pressure.
Getting boosters was to ensure hospitals were not overwhelmed.
A big boosters campaign would be run over February, and more details would be provided by the Ministry of Health.
She said the boosters programme and restricions of the red level meant we were well positioned for Omicron.
Bloomfield said the vaccination levels was "an extraordinary number" and it was pleasing to see Māori rates touching 90 per cent for first dose, and over 80 per cent fully vaccinated.
He said the technical advisers had worked over the weekend to supply the advice. People who were vaccinated were well protected, but that did wane over time and that was especially the case with Omicron.
A booster would see people's protection reach the same levels against Omicron as the second dose had for Delta - which was more than 90 per cent of protection against hospitalisaiton.
He said there was good capacity and supplies of vaccinations for the rollout.
He said there was a lot of work underway to make sure the boosters were accessible for those critical workers, and the most vulnerable to Covid-19, such as the elderly and those with underlying conditions.
Bloomfield said the side-effects from the booster had been similar to the second dose - for most people they were mild and short-lived.
On boosters for 12-17 year olds, Bloomfield said he was expecting advice from the Technical Advisory Group next week.
Asked why the change was not immediate, Ardern said a bit of time was needed to change system such as the online booking system. The decision would be formalised today, and two days was "a very quick turnaround".
Ministry of Health chief science adviser Ian Town said the move to four months had been because of the waning effectiveness, and bringing it to three months was to ensure immunity was "at a peak before we face widespread community transmission. The protection will start to rise immediately, and over the [next] 14 days the antibodies will continue to rise."
Bloomfield said the planning had been done based on a very high uptake of 95-100 per cent of people getting a booster shot.
On Māori involvement in the boosters campaign, Bloomfield said they spoke to iwi and Māori providers a lot ahead of the rollout of children's vaccinations.
He said quite a large proportion of Māori had not got their second shots until fairly late last year, so moving to three months for the boosters would help Māori rates.
Ardern said the support for Māori health providers would also help with future vaccination programmes.
She said the Government had had to work with Māori providers to stand up a system that worked for Delta, and now had to adjust that for the higher case numbers but lower severity of illness of Omicron.
On the vaccine passes, Hipkins said no formal decision was made on whether boosters would be required for vaccination certificates to stay viable, but it was likely.
Bloomfield said there would possibly only be 10-15 per cent of the hospitalisation rate for Omicron that there was for Delta, based on the emerging evidence.
Charlotte Bellis saga
On Charlotte Bellis - the pregnant Kiwi journalist who has now been accepted for an MIQ spot after being earlier refused a spot - Hipkins said he had contacted MIQ to make sure her case was being appropriately handled, and was told they were already reviewing it. He had done so after another MP raised it with him.
He would not comment on whether he had breached her privacy, saying it would be inappropriate given she was considering legal action.
The PM then interrupted the question.
Ardern said there would be people in distressing situations struggling with MIQ, but "on the flip side, that system has saved lives".
She said a new system was in sight, which would help remove that bottleneck - her announcement on the borders was due on Thursday.
Asked about other pregnant women, Ardern said there was an emergency allocation system, but "what is going to make the biggest difference here is not having to rely on MIQ in the same way".
On opening to Australia before the rest of the world, she said there was an advantage in the shorter flights - making it less likely someone would be infected in transit - but Omicron was widespread around the world.
Hipkins said he "regretted" that commercially sensitive information had accidentally been released in an Official Information Act request on the cost of the vaccines. That was released to Newsroom, but was supposed to be redacted.
Newsroom reported today that the Government expected to pay $36.50 per dose of the Prizer vaccine. The website said Hipkins' office had mistakenly supplied the price in documents released under the Official Information Act.
Fourth dose?
Asked about a fourth dose of the vaccine and when it might be required, Ian Town said as yet there were no trials underway on a fourth dose and the advisory group would consider it when Pfizer sent advice.
On rapid antigen tests, Bloomfield said there were forward orders out to the end of June. Yesterday's announcement of 36 million extra doses had only related to those secured for the short term.
On the fourth dose, Bloomfield said some people who had had a third dose during the main rollout because they were immunocompromised would get a fourth dose - it would qualify as their booster shots.
Today's cases
There are 142 Covid-19 cases in the community today.
Today's new community cases are in Northland, Auckland, Waikato, Lakes, Bay of Plenty, Taranaki, Hawke's Bay, Nelson Marlborough, and Canterbury.
The Taranaki cases were first announced yesterday but are included in official case numbers today.
Fifty-four new cases were identified at the border.
Six people are in hospital with Covid-19. One is at North Shore, three are in Middlemore, one is in Auckland and one person is in Waikato Hospital.
No one is in ICU or HDU.
Breaking down today's case numbers, 11 are in Northland, 103 in Auckland, 12 in Waikato, two in the Lakes DHB area, five in Bay of Plenty, three in Taranaki, one in Hawke's Bay, two in Nelson-Marlborough and three in Canterbury.
Ten of the cases in Northland are linked to previous cases and investigations are underway to link the remaining case.
Of the Northland cases, nine are in Kerikeri, one is in Whangārei and one is in Kaikohe.
In Auckland, there are 103 cases. Health and welfare providers are supporting 1284 people in the region to isolate at home, including 515 cases.
Of the 12 cases in Waikato, a number were unlinked and case investigations were underway to determine a source of exposure.
The two new Lakes cases are in Rotorua, the ministry said in a statement.
One is linked to a previous cases and the other was under investigation.
In the Bay of Plenty, three of the five cases are linked to previous cases while investigations are ongoing for the remaining two.
All five cases are in Tauranga.
The one new case in Hawke's Bay is linked to a known case and any associated locations of interest would be published on the Ministry of Health website.
The two new cases in Nelson-Marlborough are both linked to existing cases.
Two of three the new cases in Christchurch, Canterbury were announced yesterday, the ministry said.
Following data reconciliation, there are now nine total active cases in Canterbury, the health ministry said in its statement.
The average age of those in hospital with Covid-19 is 57.
Sixty-nine per cent of those due for their Covid-19 booster have now had it with 38,332 booster doses administered yesterday.
The total number of booster doses given to date to is 1,362,811.
Yesterday, 8,636 paediatric doses of Covid-19 were given and 37 per cent of eligible 5-11 years have now had their first dose.
Twenty per cent of eligible Māori children, aged 5-11, have received their first dose.
Twenty-seven per cent of eligible Pacific children have also had their first dose of the paediatric vaccine.
Overall, for the adult vaccine, 94 per cent have now received two doses of the Covid-19 vaccine. A year ago, that figure would have seemed very ambitious, Ardern said.
"Those high rates helped stop a Delta outbreak and have given us a headstart on Omicron." She said it was now important to get as many people as possible boosted, before Omicron was too widespread.
Eighty-five per cent of eligible Māori, aged 12+, and 94 per cent of eligible Pasifika have had their second dose of the vaccine.
New cases identified at the border (54) had arrived from: Australia, Egypt, Germany, India, Iran, Italy, Lebanon, Pakistan, Singapore, South Africa, Sri Lanka, United Arab Emirates and the US.
There are 994 active cases in the total, which are cases identified in the past 21 days that have not yet recovered
Meanwhile, InScience owner Ann-louise Anderson, whose company imports rapid antigen tests, has been sourcing products approved last week and expected to have them available to sell to companies by the beginning of next week.
She claimed for months the Government had been sitting on "lots and lots of approvals" for RATs which had met their minimum approval criteria and had only approved them last week when there was suddenly a need.
"The quite a few million more (tests) came from the ones that were newly approved and those approvals and all of those features of those products have been the same for the last year."
National leader Chris Luxon told RNZ that Australia had already approved more than 60 different suppliers of RATs, while New Zealand had approved fewer than 10.
He said New Zealand should today approve those other 50 tests Australia was already using and also enlist the help of big companies in the private sector such as Air New Zealand, Mainfreight, Foodstuffs and Zuru to help procure supply.
Ultimately National wanted RATs to be available in schools, but also for everybody to buy from the supermarket and in pharmacies.
Deputy Prime Minister Grant Robertson told RNZ this morning that orders for RATs had been placed since October and the focus was on making sure they had enough for the first two phases of its three-phased Omicron plan announced last week.
The Government announced yesterday that 55 million tests would be in the country by March with a total 123 million due to arrive in the country by June.
PCR testing was still the preferred form of testing at the moment, but in the second phase RATs would be used first for critical workers before stretching to the general public.
However Robertson said there was a global shortage of rapid antigen tests (RATs).
Yesterday, the Government announced it had ordered tens of millions of rapid antigen tests.
Physicist Dr Dion O'Neale and immunologist Dr Dianne Sika-Paotonu both welcomed the addition of more rapid tests.
"It is critical we slow down Omicron's spread throughout our communities for as long as possible and to avoid our hospitals from becoming overwhelmed as they have become in Australia and other countries," Sika-Paotonu said.
Associate Minister of Health Dr Ayesha Verrall said 36 million extra rapid antigen tests had been secured.
She said when the Omicron outbreak peaked, Kiwis might need nine million tests a week.
Today's new cases and booster announcements will precede a decision on international borders.
On December 21, the phased border reopening was postponed as the Omicron strain of Covid-19 started circulating globally.
Grounded Kiwis spokesman Martin Newell told the Herald he expected a border reopening of sorts would be planned for the end of this month.
He added: "We'll wait until that actually happens. We'll believe it when we see it."
