Taranaki residents who have recently returned from Australia are being urged to get tested for Covid-19 after traces of the coronavirus were detected in the region's waste water.
More testing of waste water is being completed today and so far no frontline workers in the region have tested positive for the virus.
Meanwhile, there are three new Covid cases today in managed isolation to report.
The investigation into the New Plymouth wastewater Covid trace results is continuing, the Ministry of Health said, adding the results could be from recently recovered cases continuing to shed the virus or undetected community cases.
"In order to determine whether there are any undetected cases the ministry is recommending anyone in Taranaki, or who has visited recently, and who has symptoms to get tested," the ministry said.
"Additional testing capacity has been stood up in New Plymouth to support potential demand."
Results for further wastewater sampling were being carried out today in Taranaki and were expected back on Monday, the ministry said.
All tests of port workers and nurses have so far returned negative results.
New Plymouth deputy mayor Richard Jordan said he understood it was very unlikely the trace results of Covid-19 were through a connection with port workers.
"Apparently it's quite unlikely," Jordan said.
"It's more likely that someone who has recovered from Covid has either travelled to Taranaki or moved to Taranaki and they're still shedding Covid. That's my layman's understanding of that."
The deputy mayor said the community was "surprised" by the news last night and there has been a surge in tests today.
"We've had these results before and they've turned out that they were clear so it's a matter of time over the next few days that we get a clearer picture," Jordan said.
"But we do encourage the community to continue to do the contact tracing and if they feel unwell to go and get a test."
Jordan said the local DBH has been proactive in encouraging the community to get tests if they do feel unwell.
Anyone who had returned from Australia and was now in Taranaki, but had not experienced symptoms, should also get tested, the ministry said.
Last night, the Ministry of Health said officials were investigating whether any recovered cases who live in the New Plymouth area had recently left a managed isolation facility.
Otago University epidemiologist Michael Baker said a community outbreak couldn't be ruled out but was very unlikely.
"That's why wastewater testing is done. If there is an undetected outbreak there ... it's an additional back-up measure," Baker said in response to the wastewater results.
The epidemiologist said the results were most likely from recovered cases continuing to shed the virus, which was going into the sewer.
"People could be positive for months after they recovered. You can detect RNA for six months after and that means they are not infected with the virus, but were still shedding fragments."
But he said it was possible someone who was back from quarantine-free travel from Australia was living in New Plymouth and was infected, and was potentially infecting other people.
Another possibility could have been shipping crews who transferred from Auckland to New Plymouth and had infected staff there.
"They are retesting those staff that previously had tested negative ... it is a possibility but it's very unlikely. "
It could be someone who lived in New Plymouth or someone who was just passing through.
As well as the three new MIQ cases, there are also two historical cases of the virus in MIQ, the Ministry of Health said in an update released this afternoon.
Ten previously reported cases have now recovered, bringing the total number of active cases in New Zealand to 75.
Of the three new cases in MIQ, one arrived from the Philippines via Australia on July 11. They tested positive after a return check on day 12.
The second case came from Mexico via the US and arrived in New Zealand on July 19 and tested positive on day three of routine testing.
The other case came from the UK via Qatar and arrived on July 22. The traveller tested positive on day one of their MIQ stay.
The two historical cases in MIQ were in the same bubble and arrived on July 21 from Russia.
There were 19 new cases of Covid-19 reported in MIQ yesterday and none in the community. The 19 new cases are all mariners in isolation.
On Thursday night, genome sequencing of the crew on the Mattina confirmed they had the Delta variant.
In total there are now 15 positive Covid cases on that ship. All crew who test positive will remain quarantined on-board.
The crew members, including the captain, have tested negative and were safely transported to on-shore facilities.