National leader Christopher Luxon says the government went into a go-slow mode around Covid-19 over the summer, and urgently needs to increase availability of rapid antigen tests.

He said New Zealand had the slowest vaccine rollout in the developed world last year and was now the fourth slowest in the developed world for boosters.

"Things have been very slow, and as a result we aren't prepared for where we need to be," Luxon said today at the Orewa Surf Lifesaving Club.

Prime Minister Jacinda Ardern announced this morning that the whole of New Zealand would move into the red light Covid-19 setting at midnight tonight.

The move comes after nine Covid-19 cases reported in Nelson yesterday were confirmed as the Omicron variant.

Luxon said rest homes, retirement villages and at-risk communities should be inundated with boosters.

He also wanted the availability of rapid antigen tests to be increased and intensive care capacity upgraded.

There were 4.6 million rapid antigen tests in the country as of 18 January.

"Rapid antigen testing, we've been talking about it for months ... it's coming, but we don't have widespread distribution of multiple kits freely to people," he said.

"We need to scramble and secure those tests, we need to get them here as quickly as possible."

In today's media conference, Ardern said rapid antigen testing had an effectiveness up to 80 percent.

She said when he had much higher cases, the government would transition from the current way of operating to "different use of testing mechanisms" and more details would be provided on Wednesday.

Luxon said the government's Covid-19 response had been confusing for the public.

"There's a big difference between PR spin and actually getting it done," he said.

"We need to get very very focused on delivery, getting things done, and execution.

"Anything that helps slow it down and helps us get prepared ... the defences aren't in place, and we haven't been protecting the vulnerable as well as we can."

Greens, experts respond to move to red

The Green Party said the success of the red traffic light level would depend on the support made available to the most vulnerable.

Covid-19 spokesperson Elizabeth Kerekere said the government must prioritise Maori and Pacific providers in the rollout of the vaccination to children and those eligible for boosters.

She also wanted to see N95 masks made freely available to the most vulnerable.

Epidemioligist Michael Baker said he was disappointed Omicron is already in the community - and believed more could have been done to keep it out for longer.

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Michael Baker Photo: RNZ / Samuel Rillstone

Baker had called for more restrictions at the border because so much Omicron was coming into managed isolation facilities.

"It would have been very valuable because we are really now in a huge race to get boosters offered or taken up by New Zealanders and to vaccinate children," he said.

"Those things are really a priority, but they will still take a couple of months to get high coverage."

However, Baker said the country was well placed to deal with the outbreak compared with others.

He had previously called for the government to delay re-opening the border by a couple of months and also reduce arrival numbers because of the high number of Covid-19 cases being detected in managed isolation and quarantine.

Microbiologist Siouxsie Wiles said it was yet to be seen how effective the traffic light system would be against the more infectious Omicron variant.

It was important to remember that this virus is spread through the air and that people could be infectious before they realised they were infected, she said.

"Transmission through the air does mean some environments are higher risk than others - especially indoor environments where people are not wearing masks," she said.

She was particularly concerned about hospitality and similar venues.

"It doesn't matter if groups of people are seated one metre away from each other, if they are indoors, especially if the place is badly ventilated, then the risk of transmission is high and we've seen lots of examples of Omicron spreading in these types of settings overseas."

Improving ventilation and introducing air-purifiers were some ways to reduce this risk, she said.

Meanwhile, retailers are asking the public to shop as normal in the coming days and weeks.

The group Retail New Zealand said the sector had been preparing for the arrival of Omicron.

Chief executive Greg Harford said the shopping environment was relatively safe through the use of masks.

He has called on consumers to shop normally during the outbreak and support the retail sector.

Today there were 24 new community cases of Covid-19 in the community, and 47 new cases in managed isolation and quarantine reported.