"In this early stage, when we're stamping it out and seeking to stamp it out, PCR remains our best solution."
Ardern said more information on a "test to return to work regime" would be outlined tomorrow, as would details on how the penultimate and final stages of the Omicron response would be managed.
The PM said high case numbers in an Omicron outbreak would lead to high exposure and contact numbers, and subsequently on critical workforce members.
Bloomfield said the Omicron response regime would involve the Government helping more businesses access RATs kits.
Ardern said testing regimes should be honed to ensure the people most likely to need tests could get tests.
"We don't want someone staying at home when they don't need to," the PM said.
Asked about critical workers, Ardern said the Government wanted to offer essential workers and their employers as much support as possible, but the expansion of rapid test use would be no substitute for prevention measures such as mask use.
"A rapid antigen test is a test. It's not a preventative measure."
On antiviral drugs, Bloomfield said orders had already been placed for Remdesivir and Paxlovid.
"The approval process is not a barrier to their use."
Booster shots
Ardern said the arrival of Omicron seemed to have encouraged many people to get the third shots today.
The PM said campaigns such as a "vaxathon" day would not be ruled out.
She said the basic message to articulate was "two shots for Delta, three for Omicron".
On booster shots, Bloomfield said the current gap of four months between second dose and booster shots was in fact relatively short by international standards.
Although some Australian states have narrowed the gap to three months, Bloomfield said in the United States the intermission was five months.
Bloomfield said when it came to gaps between first and second shots, he'd requested officials to investigate what the best interval would be for children aged 5 to 11.
Bloomfield said people at higher risk of catching Covid-19, including senior citizens, should, where possible, limit exposure opportunities.
"But I wouldn't describe that as hunkering down for the next four to six weeks," he said.
Ardern also addressed an incident when her vehicle was targeted by hostile people in Paihia.
She said she was never concerned about her safety at the time.
"We are in an environment that does have an intensity to it, which is unusual for New Zealand."
On MIQ, Ardern said international border restrictions had greatly slowed the incursion of virus strains.
"We set out that plan at the end of last year," the PM said. "It's [staged] at allowing individuals to isolate at home once they've entered the country."
"As we saw with Delta around the world, high rates of vaccination ... play a major role in preventing widespread outbreaks."
Ardern addressed media at the Beehive this afternoon.
The country is in its second full day under nationwide red traffic light restrictions, where gatherings of more than 100 people are banned.
New Zealand is currently in the first stage of the Government's planned response to Omicron.
The stage is effectively the same elimination strategy used against earlier variants, but Ardern has signalled wiping out Omicron in the medium-term will not be possible.
As a result, the Government anticipates moving to a second, transitional stage once daily cases exceed 1000, perhaps in a few weeks.
The intermediate stage is so far not clearly defined but will include adjusting health measures to focus on people at greater risk of severe illness from Omicron.
The third stage, if cases are in the thousands, will redefine tracing, contacts and isolation requirements.
Some third stage details will probably be revealed tomorrow, when Associate Minister of Health Dr Ayesha Verrall and Bloomfield are expected to address media.
Genome sequencing experts have told the Herald that refining contact definitions and more efficiently tracking contacts will be essential to stop the tracing system failing under the strain of many cases.
Ardern on Sunday indicated advice on face mask use would be assessed and updated if necessary this week.
The PM said any change to mask advice would depend on evidence gathered from overseas about which masks were most effective against the virus.
"Pfizer has provided some data to Medsafe for the rolling assessment but still needs to provide further data as it becomes available," the Medsafe site added.