New Zealand reported 12 new coronavirus cases today, all linked to an Auckland family cluster, amid the second and stronger wave of the pandemic in the country.

There was also one suspected Covid-19 case reported in Waikato, which is still under observation in a hospital, Director General of Health Ashley Bloomfield said in a daily briefing.

New Zealand has reported a total of 48 active Covid-19 cases, with 30 linked to the Auckland cluster, which has brought overall caseload in the country to 1,251, Bloomfield said.

Bloomfield said 38 people linked to the cluster were already in the Auckland quarantine facility, adding that the number is expected to grow.

"We've seen no evidence of a Covid-19 positive test outside of Auckland which is unrelated to the cluster we're dealing with," said Health Minister Chris Hipkins.

Testing had ramped up at the borders and all frontline workers will be tested by the end of Friday, Hipkins said.

Auckland resumed Alert Level 3 this week for three days, with the rest of the country going to Level 2, after 102 days without community transmission in the country.

New Zealand went to a month-long national Alert Level 4 lockdown in late March, and declared an early success of the coronavirus battle in June.

The government will make decisions and inform people of any further alert level changes at 5.30 p.m. in advance of the lockdown ending at midnight today..