A prominent epidemiologist says Wellington has "probably dodged a bullet" with the capital's Covid-19 scare, but has nonetheless called the Government's decision to extend restrictions a wise move.

Covid-19 Response Minister Chris Hipkins this afternoon announced the Wellington region would stay at alert level 2 another two days – until midnight 11.59pm on Tuesday – as local test results continued to come in.

It was also revealed the partner of the Sydney man at the centre of the incursion had now also tested positive in Australia, and may have been infected near the end of their Wellington visit or on the flight home.

No new cases in the community were reported today – a time when modellers predict that anyone who may have been infected in the capital would begin showing symptoms.

Otago University epidemiologist Professor Nick Wilson said while Wellington may have escaped an outbreak, it wasn't time to relax yet.

"The Government has made a wise decision to keep at the current alert level 2 settings for Wellington for at least a few more days – given the major problems being caused by the new Delta variant in Australia," he said.

"Also, we now know that the case who visited Wellington was able to infect others – given his partner has subsequently tested positive."

It was however reassuring news, he added, that thousands of test results for people in Wellington are all negative and that the wastewater test results for Friday had also come back negative.

Fellow Otago epidemiologist Professor Michael Baker agreed the extension was "fully justified".

"More than 2000 people were considered exposed to a potentially infectious traveller from Sydney who visited multiple crowded indoor venues last weekend in Wellington up until they left on Monday, June 21," he said.

"Given the timing, it is possible that some of these contacts are still incubating this infection and will only be identified in the coming few days, though the risk is now low."

University of Auckland microbiologist Siouxsie Wiles told The Weekend Collective that Wellington is still within the incubation period, and we are not "out of the woods yet".

She said that the news the case's partner has tested positive for Covid-19 despite being isolated from her partner shows there is cause for extending. 

"That does show the person was infectious, while they were in New Zealand and while they were travelling home."

Covid-19 modeller Professor Michael Plank said it appeared the most likely scenario was that the man entered his infectious period towards the end of his stay in New Zealand.

While he agreed it was good news that most of the 2400 contacts identified have now tested negative, it was still possible there are other contacts that were missed – such as those who hadn't been scanning in wherever they went.

"Given what we know now, finding and testing contacts from Monday morning is particularly important," he said.

"If there is even one case lurking out there, it has the potential to spread like wildfire because the Delta variant is so infectious and our vaccination coverage is too low at the moment to slow it down much."

While New South Wales had one of the best contact tracing systems in the world, Plank said it hadn't been able to keep up with the speed the virus was spreading.

The state today reported another 30 infections, bringing the size of the outbreak to 110 cases as Greater Sydney entered the second day of its two-week lockdown.

"If anyone was infected on Sunday or Monday, now is around the time they would most likely develop symptoms," Plank said.

"So it's essential you stay alert for symptoms, especially if you were in Wellington last weekend, and get tested immediately if you do feel even slightly unwell.

"High testing rates will help authorities have confidence to relax alert level restrictions as soon as possible."

For another Otago University public health expert, Dr Lesley Gray, the risk was personal.

"My family live in the Wairarapa, therefore I am concerned about the indeterminate result from Masterton," she said.

"While this could relate to the test sample not being good enough to test, it can also indicate that the test was too early to detect Covid-19 and will have to be repeated. Let's hope it is the former, and it will come back as a negative test in due course."

Gray said she'd been calling for pre-departure testing to be employed in the transtasman bubble, so was heartened to hear this was now being considered by the Government.

Wilson saw a "very strong case" for adopting a period of pre-departure testing, which could be combined with testing on arrival in New Zealand, once quarantine-free travel with Australia reopened.

"Similarly, an Australian epidemiologist has been arguing for such testing for those moving in and out of the areas under stay-at-home orders in Australia," he said.

"Results of some of these tests, like rapid antigen tests, can be available in 15 minutes and so could have minimal impact on time delays for arriving travellers."

He said saliva tests using PCR could take more time to get results – but should typically allow an infected person to be identified within at least the first day of their time in the community in New Zealand.

"The pros and cons of such different tests and how they are used to protect the transtasman bubble need urgent consideration."

That was among a raft of urgent system improvements that Wilson, Baker and fellow epidemiologist Associate Professor Amanda Kvalsvig last week called for.

They also saw a need for upgrades to our alert level, contact tracing systems, a faster vaccine roll-out, and measures to ensure Kiwis stayed home when necessary.