COVID-19: Why Health Minister Chris Hipkins didn't inform public of new case during NZ election voting

While the country was watching the election results unfold, public health officials were concentrating on another result - a new case of COVID-19 in the community.

A port worker had tested positive after carrying out maintenance on a ship in New Plymouth.

Health Minister Chris Hipkins says he had heard about the case just after 6pm on Saturday and admits considering to release the information before voting stopped at 7pm. But he decided not to inform the public about it.

"I don't think it would have been appropriate to make that public before 7pm when the polls closed," he says.

"I didn't even have time to consider whether or not that would be consistent with the prohibition on what we can do on election day. I didn't have time to get advice on that because the timeframe was so tight."

The Auckland port worker took a test on Friday after becoming unwell. He'd been working on a ship, with international crew on board, in New Plymouth on Wednesday.

That's now on the way to Napier. And there's a second ship he worked on that officials are looking at.

The worker drove from Auckland to New Plymouth and back. It's not yet known if he stopped along the way.

Director-General of Health Ashley Bloomfield has been quick to quell concerns.

"This case has also been caught early and the risk of onward transmission has been quickly contained," he says.

Routine testing is already carried out at ports and New Zealand epidemiologist Professor Michael Baker says there's no cause for alarm.

"So we need to figure out what happened here and how can we prevent these episodes happening in the future," he says.

"But the other thing, of course, is this is showing the system working very well and it detecting this case quickly and following up."

Prime Minister Jacinda Ardern says there's no need to lockdown.

"There's nothing to suggest the need to move any of the restriction levels," she says.

Meanwhile, our one-way trans-Tasman bubble seems to have well and truly burst.

It's revealed 55 passengers who travelled from New Zealand to Sydney broke the rules and travelled on to Melbourne - not 17 as first thought.

COVID-19, continuing to cause problems at all borders.