New Zealand’s biggest city, Auckland, will stay under Coronavirus (COVID-19) lockdown until September 21, after 33 new cases were recorded in the area in the past day, the prime minister said on Monday.

Prime Minister Jacinda Ardern said three clusters were continuing to produce cases of community transmission in Auckland, compelling the extension of the hard Alert Level 4 lockdown for another week.

“Level 4 remains our best option to beat Delta and contain the virus at this stage of the outbreak,” Ardern said during a news conference after a cabinet meeting.

“We don’t want to risk the sacrifices everyone has made, and all the hard work put in, by moving to Alert Level 3 too quickly,” she added.

The rest of the country would stay at Level 2 until September 21.

At that point Auckland was expected to move down a notch to Level 3, although this was dependent on the course of the city’s outbreak, Ardern said.

He added that the cabinet would review the Coronavirus situation in the coming days.

Over the course of the pandemic New Zealand has been pursuing an ambitious, but contentious, strategy to totally stamp out COVID-19 transmissions, relying on border closures, lockdowns, and testing.

On August 17, all of New Zealand was moved to Level 4 the highest level within hours of a single case being detected, with all schools and non-essential businesses closed.

The outbreak has produced 955 cases so far, local media reported.

But last week, as numbers declined, all of the country except Auckland moved out of the hard lockdown.