New Zealand is keeping its largest city under strict lockdown for at least another week. Officials said Monday that the 1.7 million people living in Auckland will remain under strict movement restrictions as part of the wider plan to control the spread of the more contagious Delta variant of the coronavirus.

As of Monday, 33 new cases of the COVID-19 had been reported in Auckland. This was a significant jump from the 23 reported on Saturday and the 20 cases on Sunday.

New Zealand Prime Minister Jacinda Ardern said during a news conference that the lockdown measures already in place in Auckland will be extended until Sept. 21. Health authorities have ruled out a widespread transmission of the virus in the city but Ardern decided on keeping the lockdown in place as long as new cases keep on emerging.

Ardern said that if cases subside, the lockdown in Auckland will be downgraded from level 4 to level 3. The less strict lockdown level will allow some movements within the city but schools, offices, and other public venues will remain closed down.

Throughout most of the pandemic, New Zealand has remained largely virus-free. However, an imported case of the disease had arrived in the country last month, prompting the government to order an immediate nationwide lockdown.

Since the first case was detected on Aug. 17, the number of new cases has ballooned to 955 positive infections. Health authorities said most of the new cases were detected in Auckland.

The rest of the nation had been downgraded to a Level 2 lockdown since last week. Auckland has remained cut off from the rest of the country.

New Zealand's quick action in response to the pandemic, including its immediate international border closure, has been credited with its low infection rate. Since the start of the pandemic, the country has only reported a total of 3,593 cases and 27 deaths. Despite its low infection rate, Ardern's government has been criticized for its slow vaccination rollout. As of this week, only 34% of the country's 5.1 million-strong population has been fully vaccinated.