Traces of the Covid-19 virus have now been detected in wastewater systems in four cities: Wellington, Christchurch, Rotorua and Queenstown.
There is one new case of Covid-19 in managed isolation reported today by the Ministry of Health.
The case was picked up during day 1 routine testing of a person who came from India via Qatar.
The Ministry of Health said wastewater tests had recently detected weak positive results in Wellington, Christchurch, Rotorua and Queenstown.
Subsequent testing has been undertaken from which Queenstown and Wellington have returned negative results. Further testing in Christchurch and Rotorua is underway.
The ministry said its current assessment was that the weak positive results were likely from recent positive cases in managed isolation or due to recently recovered cases who are not infectious but continue to shed the virus after returning home or while travelling.
There is no risk of infection from Covid-19 in wastewater.
Director-general of health Dr Ashley Bloomfield said wastewater testing served as an early warning system in the fight against Covid.
"When wastewater testing returns weak positives, it's essential that anyone in these areas with symptoms consistent with Covid-19 stay at home and promptly call Healthline (0800 358 5453) about getting a test," he said.
"Any cases of Covid-19 need to be detected quickly in order to stop the virus spreading in our communities. This is especially important as we head into winter, as people may have the usual winter coughs and colds."
The ministry said a previously reported case had now been reclassified as historical, taking the total number of historical cases identified this year to 61.
The total number of active cases in New Zealand today remains at 24.
The ministry urged everyone in New Zealand to continue using the NZ Covid Tracer app and keep up hygiene measures including wearing a face covering on public transport, washing your hands, and coughing or sneezing into your elbow.
Meanwhile, more than 500,000 doses of the Covid-19 vaccine will have been delivered to New Zealanders by tomorrow.
Yesterday the Ministry of Health said six people had tested positive in managed isolation and had been moved to quarantine.
One of the new cases flew in from India on May 14 and tested positive to Covid on their day three routine testing, while two others flew in from Qatar on May 14 and 15 and tested positive on days two and three of their stay in managed isolation. The other three cases arrived from Bahrain, Turkey and Maldives and tested positive on their day 0 routine testing.
On Tuesday one person in managed isolation tested positive and on Monday it was five.
That brought yesterday's number of active cases in New Zealand to 25.
Covid-19 Response Minister Chris Hipkins said yesterday that 474,435 doses of the vaccine had been administered and the 500,000 dose mark would be reached by tomorrow.
He said more than 152,000 people were now fully vaccinated.
He also announced a $1.4 billion fund over two years would ensure vaccines were free for every New Zealander.
Almost $1b had been allocated for vaccine purchase agreements, $66.3 million for specialist vaccine equipment and the remaining $356.9m was for technology to support the roll-out.
Auditor-General John Ryan also released a report yesterday into the vaccination rollout, saying a "significant scale-up" was needed if the Government was to hit its vaccination goals.
Even if everything ran according to plan, the goal would only just be achieved, he said.
Last week the rollout was ahead of the delivery target, with just over 120,000 people having had two vaccines doses.
The real challenge would come when larger supplies of the Pfizer vaccine arrived from July.
"I am not yet confident that all the pieces will fall into place quickly enough for the programme to ramp up to the level required over the second half of 2021," Ryan said.
It comes as a vaccination centre in Ōtara said it may have to cut the number of days it operated unless it urgently got more vaccinators.
Ryan noted there were "significant risks" around the number of vaccinators, the distribution model to ensure doses were delivered to the right place and at the right time, and ensuring that Māori, Pasifika, people with disabilities, and hard-to-reach communities were vaccinated.
Hipkins responded by saying it was an ambitious rollout, and he was confident but nervous about it.
"We are going to be pulling out all the stops to make sure that everybody can have a vaccine by the end of the year."