"Once you are getting up to 800 cases a day, that is really beyond the realm where we can expect public health to be doing our contact tracing for us," O'Neale said.
"So at that point people who have noticed they've got symptoms or have got a positive result, you want them as soon as possible to notify all their contacts - don't go and wait for public health to tell you what to do."
Phase 2 marks a significant shift in the Omicron response, moving to minimising and slowing further spread and looking after vulnerable populations rather than the "stamp it out" approach of Phase 1.
It includes greater use of rapid antigen testing (RATs), shorter isolation times, and "self-service" for lower risk positive cases - meaning people will take care of themselves rather than get intensive support from public health.
RATs could be used for symptomatic people or close contacts. And "test to return" will be introduced for critical workers who are close contacts - meaning they can go back to work with a negative RAT test rather than isolate.
Isolation times for positive cases would drop from 14 days to 10 days for positive cases, and from 10 days to 7 days for contacts.
The ministry said today there were 7 million RATs in the country.
O'Neale said the rise in Covid cases today was in line with modelling.
"A jump from mid-400s to 800s is big, but once you smooth that out with a few of those days of 200s this week, it is roughly on the trajectory of where we expect things to be heading."
However, it would be alarming if cases doubled for two or three days in a row, he said.
"That would be things spreading a lot faster than we've seen in other countries," he said.
O'Neale said the test positivity rate was now around 2 per cent.
"The fact that it is going up is a little bit concerning. We saw highs in the UK and Australia of 30 per cent. But anything under 5 per cent you are still able to do some preventative testing."
Dr David Welch, senior lecturer at the University of Auckland, said today's case numbers indicated that Omicron was starting to spread more rapidly than in the first weeks of the outbreak.
"This is in line with outbreaks overseas where case numbers have doubled approximately every three days," he said.
"The early spread here was likely limited by contact tracing efforts but with higher case numbers, contact tracing is not able to keep up."
The virus was now spreading through the country. The latest data showed 19 out of 20 DHBs had reported positive cases.
"We can continue to limit the impacts of spread by following the basics of mask-wearing, getting tested if symptomatic, meeting only in well-ventilated spaces, getting vaccinated and boosted, and scanning in wherever we go," Welch said.
"Anyone who is eligible for a vaccination or a booster shot should get it as soon as possible as we are all likely to encounter Covid in the coming weeks."
