New Zealand identifies Delta outbreak origin as cases jump

New Zealand's COVID-19 outbreak jumped to 21 cases on Thursday, but the authorities said the virus may not have been in the community for long as they linked its origin to a recent returnee from Sydney.

Prime Minister Jacinda Ardern and Health Chief Ashley Bloomfield told a news conference 11 new cases had been reported over the past day.

Ardern said genome sequencing revealed the current positive cases were a close match to a returnee from Sydney who arrived on a flight on August 7.

The person tested positive to a COVID-19 on August 9 and was moved to a quarantine facility. He was later moved to a hospital on August 16.

"This is a significant development. It means now we can be fairly certain how and when the virus entered the country," Ardern said at a news conference.

"And based on timelines there are minimal, possibly one or maybe two, missing links between this returnee and cases in our current outbreak. And the period in which cases were in the community were relatively short," she said.

New Zealand had been virus-free and living without curbs until Ardern ordered a snap three-day nationwide lockdown on Tuesday after a new case was found in the largest city Auckland.

The new cases, though still relatively small in number, have caused significant concern for authorities in the nation, which has struggled to get its population vaccinated.

On Wednesday, New Zealand's central bank delayed a widely expected interest rates hike, citing increased economic uncertainty caused by the outbreak and new lockdowns.

Ardern warned that without nationwide curbs, New Zealand could witness the chaos seen in neighbouring Australia where the fast-spreading Delta variant has thrown half the country into lockdown.

A poor vaccination record, with just over 20 per cent of the 5 million population inoculated against COVID-19 so far, meant the risk of exposing large number of people was higher.