New Zealand’s government said it will extend a strict nationwide lockdown until at least Friday as it tries to extinguish a growing coronavirus outbreak.

The news came as health authorities reported 35 new local infections of the fast-spreading Delta variant, the highest number of daily Covid-19 cases in New Zealand since April last year.

First discovered last week, the outbreak has grown to 107 cases.

But health authorities say they have found links among most of those cases, giving them hope they can quash the outbreak.

Authorities said they have tested about 3% of the nation’s entire population over the past six days.

The country’s prime minister Jacinda Ardern said the lockdown will continue until at least the end of the month in Auckland, where most of the cases have been found.

“We do need more information.

“We need more certainty.

“We don’t want to take any risks with Delta,” Ms Ardern said.

“If the world has taught us anything, it is to be cautious with this variant of Covid-19.”

Ms Ardern said modelling suggested the outbreak should peak in a few days’ time, and then decline.

One of the reasons lockdowns are considered essential in New Zealand in that inoculation rates remain low, with only about 20% of people fully vaccinated.

The strict lockdown means most people must remain at home, leaving only to buy groceries or medicine, or to exercise.

Ms Ardern also announced that the government has decided to suspend regular Parliament sessions for a week, a move that drew criticism from opposition politicians.

“At a time when New Zealanders have the harshest lockdown in the world and have lost our freedoms because of the government’s failure to vaccinate and secure the border, this move by Jacinda Ardern is unfathomable,” said Judith Collins, the leader of the opposition.

While New Zealand was maintaining its strategy of trying to wipe out the virus completely through lockdowns, neighbouring Australia appeared to have conceded that lockdowns would not be able to eliminate the Delta variant entirely and could only slow its spread.

Australian prime minister Scott Morrison said lockdowns are “not a sustainable way to live in this country”.

He said states must open their borders once vaccination rates reach 80% of the population aged 16 years and older.

His remarks came as an outbreak in Sydney grew by more than 800 cases, near record levels.

Health authorities said an outbreak centred in Melbourne also grew by 71 cases and another in the capital, Canberra, grew by 16 cases.

All three cities remained in lockdown.

But in Western Australia, where there are no community infections, premier Mark McGowan said his government would not reopen at the 80% vaccination level if it meant reintroducing the virus.

About 24% of Australians are fully vaccinated.