There are no new Covid-19 cases to report in the community today, the Ministry of Health has confirmed.

So far 2213 people have been identified as contacts of the man who visited Wellington last week and later tested positive for Covid-19.

Of those contacts, 1441 have returned a negative result, the ministry announced this afternoon. A further 764 are either being followed up or are awaiting a test result. Eight have been "excluded from testing".

There were 58 passengers on Qantas flight QF163 that the man took to Wellington last Saturday. All have been advised to self-isolate. Thirty-five have returned a negative test result, with the rest expected in the next couple of days. Another eight passengers are the people the ministry said were excluded from needing a test.

Two travellers transferred to MIQ

The ministry has also announced that two people who arrived from Australia yesterday are in managed isolation in Auckland, after it was found they weren't eligible for quarantine-free travel.

One person, travelling from NSW, transited to Auckland through another Australian port and was "detected by Customs officials". The other person is an Australian resident who cleared Customs through the e-gates but then realised they may not be eligible for quarantine-free travel. They rang Healthline for advice.

Auckland Regional Health's Medical Officer of Health says both passengers are a low public health risk, but they will spend 14 days in managed isolation.

Demand for Covid-19 tests in greater Wellington is "steady", the ministry said. Yesterday 2345 tests were processed in the region.

Anyone at a location of interest or who is symptomatic has been told to ring Healthline on 0800 358 5453 for advice on testing and how to book a test.

The ministry is asking people to book in advance at all testing sites, and has opened additional testing locations today - with information available on DHB websites or Healthpoint.

On Friday, 8593 tests were processed nationwide.

Today the ministry reported four new Covid cases among recent returnees in managed isolation: one person who arrived on June 12 from India, and people who arrived on June 24 from Indonesia, Dominica and Ghana.

There were nearly 960,000 scans using the Covid Tracer app in the 24 hours to midday yesterday, which the ministry said was a "healthy increase". It was "incredibly important" for people to keep a record of where they had been, the ministry stressed.

Aus traveller has Delta variant

Last night it was confirmed the man who tested positive for coronavirus after travelling to Wellington from Sydney has the more infectious Delta Covid-19 variant.

"The confirmed case that travelled to New Zealand is linked to the Bondi cluster, which has been confirmed as the Delta Covid-19 variant," a NSW Health spokesperson said.

"The person accompanying the confirmed case of Covid-19 who travelled to New Zealand from Sydney tested negative on return to Australia and was not infectious while in New Zealand."

Wellington was put into alert level 2 this week, which will remain in force until at least 11.59pm tomorrow. Ministers will meet tomorrow morning to decide any changes to alert levels.

So far there have been no positive results after thousands of tests across the region.

Leading scientists have previously told the Herald that positive test results from anyone who caught Covid-19 from the Sydney tourist in Wellington are most likely to have emerged yesterday and today.

However, New Zealand's director of public health Dr Caroline McElnay last night said the Delta variant confirmation reinforced the Government's precautionary approach regarding the Covid-positive traveller to Wellington.

"The signs so far are encouraging. Testing has ramped up and there have not been any community cases at this point," McElnay said.

"But I want to emphasise the importance of staying vigilant, stay home if unwell and get advice about having a test, wash hands regularly, cough and sneeze into the elbow, wear masks or face coverings on all public transport, and keep track of where you've been – scan QR codes wherever you go and turn on Bluetooth tracing in the app dashboard.

"It's incredibly important people keep up to date with the ministry's locations of interest in Wellington and if you've been at one, to continue to isolate either for the full 14 days and get at least two negative test results or to isolate until a negative day five test, depending on your situation."

Earlier on Friday, NSW Premier Gladys Berejiklian announced large parts of Sydney were heading into a lockdown, with a stay-at-home order lasting until midnight next Friday.

Covid-19 Response Minister Chris Hipkins and director general of health Dr Ashley Bloomfield. Photo / Mark Mitchell

"It's incredibly important people keep up to date with the ministry's locations of interest in Wellington and if you've been at one, to continue to isolate either for the full 14 days and get at least two negative test results or to isolate until a negative day five test, depending on your situation."

Earlier on Friday, NSW Premier Gladys Berejiklian announced large parts of Sydney were heading into a lockdown, with a stay-at-home order lasting until midnight next Friday.

What we know about the 'Delta' variant

The Delta variant of the Sars-CoV-2 coronavirus – scientific name B.1.617.2 – has spread to 80 countries since first being detected late last year, and is thought to be partly responsible for India's disastrous second wave this year.

"We know that it's a lot more transmissible – in fact, it's about twice as transmissible as the original variants of Covid-19," Professor Michael Plank, a modeller at Te Punaha Matatini and Canterbury University, told the Herald's science reporter Jamie Morton (read the full explainer piece by clicking here).

"We're still learning about exactly why that is - there's probably a range of factors – but we know from data on things like contact tracing, the proportion of contacts that get infected with this variant is higher."

Plank said New Zealand's lack of restrictions on movement and contact under level 1 would make it an "ideal environment" for the virus to spread virally.

"And as we are still in very early stages of the vaccine roll-out, the immune levels at the population level are still very low."

He also added studies have shown the virus spreads up to 40 per cent faster in winter than summer.

"So this elevates the risk of transmission in New Zealand right now, especially in indoor or poorly ventilated environments."

A study by University of Edinburgh researchers published in The Lancet suggested the variant carried around double the risk of hospitalisation compared with the Alpha variant.

Research has also shown that in community cases at least two weeks after the second dose, the Pfizer-BioNTech vaccine that most Kiwis will receive was found to provide 79 per cent protection against infection from the Delta variant, compared with 92 per cent against the Alpha variant.