New Zealand confirms UK COVID-19 strain as Auckland lockdown begins

New Zealand health authorities have confirmed the coronavirus cases that sent Auckland into a sharp three-day lockdown were the more infectious UK variant.

After learning of three new community cases in Auckland, Prime Minister Jacinda Ardern and her cabinet met on Sunday afternoon to slap the restrictions on New Zealand's biggest city.

Those cases — from one Auckland family — mean 1.6 million Kiwis face bans on non-essential movement until midnight on Wednesday as part of alert level three restrictions.

On Monday morning, Ms Ardern said genomic sequencing showed the virus was one of the slightly more infectious strains.

"We were right to take a cautious approach and focus on safety because we've confirmed it is the UK variant," she told Radio NZ.

"Based on that sequencing we haven't been able to link it to any of our managed isolation facilities ... it wasn't someone who went from an airline into our managed isolation."

Ms Ardern said health officials were still trying to identify the source of infection, working on two main leads.

As one of the new community cases worked at a business servicing airlines at Auckland airport, officials are looking at whether the virus may have slipped out through a transit passenger, or via laundry of air crew.

"There may be a scenario where we aren't able to answer what happened here," Ms Ardern warned.

Australia has halted quarantine-free travel for New Zealand for an initial three-day period, starting Monday.

Australia's medical experts met on Sunday night to declare New Zealand a red zone, meaning people arriving from New Zealand will need to go into hotel quarantine for 14 days.

The lockdown is the second time Auckland has undergone the emergency measures since last year's more stringent 51-day nationwide lockdown which helped New Zealand eliminate the virus.

The rest of New Zealand has been placed at alert level two, which mandates social distancing, caps on gathering and increases mask wearing.

It is not yet clear whether the lockdown will extend beyond midnight on Wednesday.