There are no new cases of Covid-19 in the community today and two in MIQ, the Ministry of Health says.

There are also two new historical cases on board the Spanish fishing vessel Playa Zahara. The number of active cases in New Zealand is now 58.

The update comes as the ministry scrambles to determine whether two positive wastewater results this week in Taranaki mean there are undetected cases in the community.

People in the region are being urged to get tested, as well as anyone who has recently visited and who has symptoms.

The ministry is recommending anyone who has recently been in Australia who is now in Taranaki to get tested - even if they don't have symptoms.

Any recent returnees from Australia who have Covid symptoms are advised to get tested and continue to check the state websites for locations of interest.

Forty-five people associated with cases in Australia, who are now in New Zealand, have returned negative test results.

The ministry would not be providing an update on the number of people who have been tested for Covid-19 in Taranaki until tomorrow. It said it was "pleased" at the response to the call for testing in New Plymouth.

Additional testing capacity has been set up in the region.

Results from "further and wider" wastewater sampling carried out this weekend in Taranaki were also expected tomorrow.

Movements of mariners aboard the Playa Zahara and Viking Bay vessels docked at Port Taranaki in New Plymouth do not appear to be a factor in these wastewater detections, the ministry said.

Additional tests of port workers and nurses who have possibly been in contact with mariners have come back negative so far.

The two positive wastewater results were taken on Monday and Thursday this week.

They could be because of recently recovered cases continuing to "shed" the virus, the ministry said yesterday.

"Wastewater testing is very sensitive and can pick up if they've had the virus previously," Deputy Prime Minister Grant Robertson told TVNZ's Q+A this morning.

"That's still regarded as the most likely scenario at play here but we want to cover off all our bases."

Update on infected mariners

Six crew members from the Viking Bay vessel, docked at Queens Wharf in Wellington, have returned to the boat from managed isolation. There are now 10 crew members in quarantine on board, up from four yesterday. Ten remain in MIQ onshore in Wellington.

All crew onboard the Playa Zahara have recovered and are back on board the ship docked in Lyttelton. One crew member has returned home.

There have been no changes to cases aboard the Mattina. Fifteen positive cases remain on the vessel. Five crew who tested negative have been transferred to MIQ onshore.

Yesterday's Covid cases

Three positive cases and two historical cases were reported in managed isolation facilities yesterday.

Among them were recent returnees from Mexico via the United States, Russia via Singapore, the United Kingdom via Qatar, and the Philippines via Australia.

Australia

New South Wales has recorded 141 new locally acquired Covid-19 cases today and two more deaths due to the virus.

Thirty-eight of today's community cases were infectious while in the community.

Yesterday, 163 new cases were recorded. Forty-five were infectious while in the community.

Victoria has recorded 11 new Covid-19 cases overnight. However, all cases are linked to the current outbreaks. This brings the state's number of active cases to 179.

All positive cases were in quarantine throughout their entire infectious period.

Robertson said the transtasman travel bubble would only re-open if community transmission of the Delta variant was "contained".

It was paused for at least eight weeks on Friday, giving New Zealanders seven days to return home.