The first phase is the one we are in now, and includes an intensive approach to contact tracing.

Under the second phase, the focus will shift to people who are more at risk, and critical workers.

"This is ultimately about ensuring the wellbeing of all New Zealanders. This has been the principle of our Covid-19 response right from the beginning."

Dr Verrall says New Zealanders step up when there's a job to do, and our high vaccination rates, the hard work the public health team and the traffic light system meant New Zealand could do what many countries around the world could not.

"We reduced the spread of Delta, emptied our ICU of Covid cases, and we're now in a good position to manage the spread of Omicron."

She says Omicron is the most transmissible variant and will spread fast, putting our health system and infrastructure under considerable pressure. She says new reports suggest Omicron cases double every two to four days, which meant a 10-case outbreak could mean more than 1000 cases per day within six to 12 days.

"It's important to remember that Covid-19 is markedly different to what it was in the beginning of the pandemic."

The new three-phase public health response to Omicron will include reducing the isolation period for cases and close contacts at Phase Two and Three to 10 and seven days.

There will also be increased use of rapid antigen tests and automated contact identification.

New Zealand is currently in the first phase, says Dr Verrall.

"Broadly speaking, that includes the same contact tracing, isolation, and request that everyone who is symptomatic be tested at a community testing station or at a primary health provider.

"Our objective is to keep cases as low as possible for as long as possible to allow people to be boosted and children to be vaccinated without Omicron being widespread."

Phase Two will be designed to slow the spread and protect the country's vulnerable communities.

"The system will be adjusted to focus much more on identifying those who are at greater risk of severe illness from Omicron - which will be a smaller percentage of cases.

The isolation period in this phase will be 10 days for cases and seven days for contacts.

"Household contacts will actively be managed by contact tracing services, with close contacts requiring a PCR test on day five.

"A rapid escalation in case numbers and the resulting pressure on our resources will also require us to shift from identifying all infected individuals to being more targeted to those most at risk and those needed to keep the country going."

Dr Verrall says there would be an increased use of digital technology in this phase.

"Cases will be notified via text message and be directed to an online self-investigation tool which will focus on high risk exposures. Information will be provided via email and phone based interviews will still take place where it's required."

She says rapid antigen tests (RATs) will be integrated into the country's testing system at this phase and will work alongside PCR tests.

"They will be useful when the laboratories cannot provide PCR results within a useful time frame because of large volumes or because of transport delays."

In Phase Three, when cases are in the thousands, there will be further changes to contact tracing.

"The definition of contacts will change to household and household like contacts only. This will mean the highest risk contacts will need to isolate.

"Supported self-service, rapid antigen testing for diagnosing Covid and a self-service tool to enable identification of high risk contacts will be significant to respond to the high volumes of Omicron cases."

The new announcements came after the government set out new rules for mask use and gave an update on the testing strategy yesterday.

The plans have already attracted criticism, with opposition parties accusing the government of taking rapid antigen tests (RATs) from the private sector and treating the public like children.

On international borders reopening, Cabinet ministers have continued to say plans set out at the end of last year - to reopen the border in stages from the end of February - remain unchanged despite the presence of Omicron.

This would include allowing people to isolate at home rather than MIQ when returning to New Zealand from overseas, and an update on that is expected in the coming weeks.

RNZ.