The outbreak was first identified on August 17, and is likely to have peaked a fortnight later when 83 cases were announced.

Prime Minister Jacinda Ardern has called recent case numbers "a steady decline", crediting her quickly-instituted lockdown with arresting the spread.

"We've certainly seen the role that level four has played," she said.

However, getting numbers into single digits is proving harder.

For the past fortnight, NZ cases have hovered between 11 and 33, showing the difficulty of eliminating the infectious Delta variant.

Australian leaders including Scott Morrison and NSW premier Gladys Berejiklian have openly cast doubt on New Zealand's goal of removing COVID-19 from the community.

Director-General of Health Ashley Bloomfield said reports from contact tracers in Auckland gave him hope elimination was still in reach.

"The cases are still in the teens at the moment although we're seeing them trend down," he said.

"The outbreak in wider Auckland is very much under control."

Dr Bloomfield said recent cases had largely been confined to "groupings of households in south Auckland".

'(Health officials) know the connections and therefore they're aware of where other cases may come up, and they're able to rapidly link new cases back to those households," he said.

"So that is giving us increasing confidence so the outbreak is becoming controlled."

The 13 new cases announced on Thursday were all from Auckland, which remains in lockdown to fight the spread of the virus.

Importantly, the number of hospitalisations remains largely static.

On Thursday, 19 Kiwis were in hospital with COVID-19, including four in intensive care.

While 996 have been infected in the Delta outbreak, just one New Zealander has died, an Auckland woman aged over 90 with pre-existing health issues.

Australian Associated Press