UPDATED 8.10AM: New wastewater testing in Tauranga and Mount Maunganui has come back negative, after a positive Covid-19 result from a sample taken last week.

Covid-19 Response Minister Chris Hipkins said there was no confirmed theory on what caused the earlier positive test.

But if there was a potential outbreak there would have been more positive results, he said.

There were 45 new cases of Covid-19 reported in the community yesterday, all in Auckland - a large increase on previous days.

University of Otago epidemiologist professor Michael Baker said the 12 linked cases among them was an indication of was ongoing community transmission.

Hipkins told Morning Report he was not anticipating another big number of cases today.

"It's understandable that people will look at that and think that's a lot of extra people, but the vast majority of those were contacts of existing cases."

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