COVID-19: Microbiologist Siouxsie Wiles says there could still be a spike in coronavirus infections

A microbiologist believes the coming days will be crucial in the fight against COVID-19 as Aucklanders brace for more test results.

The Government plunged the super city into an alert level 3 lockdown on Sunday after three cases, later confirmed to be the UK variant of the disease, were found in the community.

No additional cases were found on Monday, but officials are still scrambling to find the source and more test results will be revealed later on Tuesday.

Auckland University microbiologist Siouxsie Wiles says the number of infections could still spike.

"We know that this virus has an incubation period, generally, of around two to 10 days but for some people it can be longer," Dr Wiles told Newshub on Monday. "We may well have people that are in that incubation period and they wouldn't be testing positive yet.

"It really is just a wait-and-see."

Dr Wiles said because the infections are the mutant UK variant they are likely to spread faster.

"It's entirely dependent on whether that transmission has happened," she said. "The question will be, how big is this outbreak already?"

She noted New Zealand had been relatively lucky when it came to COVID-19.

"We're not doing this lightly - we only have to look overseas and see what happens if you don't act swiftly.

"For us, we've been enjoying an incredible summer doing things that in most of the rest of the world are just not done.

"If we do our part, hopefully, we'll be out of this [lockdown] sooner. We know that the harder we act and the faster we act, the sooner we get back to our alert level 1."

Appearing on The AM Show on Tuesday morning, Director-General of Health Ashley Bloomfield confirmed no new COVID-19 cases relating to the index infections had been found. A recent close contact of the three south Auckland cases - from Papatoetoe High School - returned a negative test on Tuesday morning.

Health officials are now reviewing border testing protocols in light of the cases to ensure any vulnerabilities are stamped out, Dr Bloomfield said.

"That's what we do in these situations - we learn and adapt and evolve the response as we go."

The Government plans to review New Zealand's COVID-19 restrictions later on Tuesday, pending test results.