WELLINGTON (BLOOMBERG) - New Zealand is bracing itself for the arrival of Omicron, with the highly infectious Covid-19 variant expected to breach the nation's closed border at any time.

"We know that with Omicron, it is a case of when, not if," Prime Minister Jacinda Ardern told a news conference on Monday (Jan 17) in Auckland.

"We're doing what we can, but I think it would be wrong for us to assume that those border measures will be sufficient. At some point, we will see Omicron in the community."

The government has delayed a phased reopening of the border to keep Omicron out while it rushes to administer booster vaccination shots and begin inoculating children.

While 93 per cent of adults are now fully vaccinated, the evidence from neighbouring Australia shows that Omicron will still lead to a surge in infections.

That will be a new experience for New Zealand, which managed to eliminate coronavirus from the community in the initial stages of the pandemic.

Even though it failed to repeat the feat when the Delta strain arrived in August last year, that outbreak has been kept in check by rising vaccination rates.

The country has recorded just 52 deaths from Covid-19.

Ms Ardern said the government is learning from other nations grappling with Omicron outbreaks as it prepares to manage its own. She urged eligible people to get a booster shot, saying it clearly provides greater protection against the variant.

Omicron cases are being caught at the border, where arrivals are required to enter managed-isolation facilities.

Over the weekend, a worker at one of the government-run sites tested positive for Omicron, though all their close contacts in the community have so far tested negative.

"It is incredibly important that we prepare as much as we can," Ms Ardern said. "There's no firm way to be able to establish how long our border measures are able to hold."