On Monday, health officials reported 27 community cases of COVID-19, but 33 cases among international arrivals during the mandatory quarantine stay.

Dozens of cases are arriving each day at the border, and are predominantly the Omicron variant, which is yet to spread widely in New Zealand.

There have been 273 cases of COVID-19 picked up at the border this year.

As of Friday, when 176 had been reported, 127 were identified as Omicron, eight were Delta and the balance were still being investigated.

A sizeable minority of the cases are coming from Australia, where the variant is rampant.

University of Otago public health professor Michael Baker said every new case contributed to the chance of a leak from quarantine, known locally as MIQ.

"We're getting more than 20 cases a day ... that's going to put huge strain on the MIQ system, as we know everyone infected that arrives increases the risk of border failure," he told Radio NZ.

The virus has also returned to Wellington, which has not had identified community transmission since August.

On the weekend, two cases were reported in the capital with links to a music festival in Tauranga held the previous week.

On Monday, another Wellington case was found with links to an out-of-town music festival - a New Year's Eve event in Auckland.

Of the 26 other community cases, most (16) were from Auckland, with handfuls in the Waikato, Bay of Plenty, Hawke's Bay and Rotorua.

There are 35 cases in hospital with the virus including one in intensive care.

Australian Associated Press