Experts say Auckland should stay at alert level 3 until the city hits a vaccination rate of 90 per cent as the chances of eliminating the Delta outbreak suffered a blow with new cases spilling into the Waikato.

Te Pūnaha Matatini data modeller Shaun Hendy says loosening restrictions in Auckland would heighten the risks of further spread not just in the city but to other parts of the country, and possibly push all of New Zealand back into level 3 restrictions.

"I'd like to see us get to 90 per cent vaccination in Auckland before we consider moving," he told the Herald.

That, however, could take several weeks at least.

"If Aucklanders really got to work and turned up to be vaccinated in numbers it could be a matter of several weeks before we saw those rates hit," he said.

There were 33 new Covid-19 cases announced today. There are two new cases in Waikato and parts of the region - including Hamilton and Raglan - will move into alert level 3 at midnight today.

University of Otago Professor Michael Baker agrees Auckland's current restrictions need to stay because little is known about how the virus reached the Waikato.

"I think it's important at this stage to get that initial info and then get the plans underway for a rapid and vigorous response," he said.

University of Canterbury's Michael Plank says the Auckland boundary will never be watertight, which means there is always the risk of cases popping up anywhere in the country as long as there is transmission in Auckland.

"The fact that the Waikato cases don't have a clear link to the Auckland outbreak and have been infectious in the community for several days is concerning. It suggests there could be additional undetected community cases."

Hendy says the best-case scenario would be a direct link between the Waikato and Auckland cases, but in the meantime moving the Waikato towns to level 3 while this is being worked out is "prudent".

Victoria University psychologist Dr Dougal Sutherland says the latest move will cause some anxiety and frustration for some, especially at the first weekend of school holidays.

But it's also a wake up-call that could be useful in pushing up testing and vaccination rates in the Waikato, if not the whole country.

Lesley Gray says the new cases being picked up by hospital and surveillance testing is concerning, because it suggests people have not been concerned about catching the virus in recent weeks.

"We all have to behave as though everyone around us is Covid-19 positive," she said.