The Government would be playing "Russian Roulette" with Kiwi lives if it exited lockdown without ramping up its contact-tracing work, an expert says.

University of Otago epidemiologist David Skegg told the Epidemic Response select committee that the country needed to be able to trace all contacts of any known cases within two to three days, as Australia has managed.

But he cautioned against too many comparisons with Australia, who have seemingly similar case numbers while under a much less stringent lockdown.

The Government is expected to make a decision next Monday on whether or not to extend or end the level 4 lockdown at the end of its initial four-week run on April 22.

Skegg said it was key that if the lockdown was lifted New Zealand had high rates of testing and rapid contact tracing of any known cases.

"As soon as the lockdown is lifted the epidemic will take off again unless we have the other measures in place," Skegg said.

Mark Metcalfe A jogger runs along Bondi Beach in Australia during lockdown.

Skegg was also keen on seeing "surveillance testing" up and running, something the Government has been talking about for weeks but is yet to formally begin.

"If the answer to those questions is 'no', I would submit that we're asking the Cabinet to play Russian roulette with the health of New Zealanders," Skegg said.

Skegg was speaking after a briefing from Australia's chief medical officer Professor Brendan Murphy, who detailed the rapid contact-tracing work Australia was able to do.

Several National MPs on the committee made the point that Australia had a seemingly similar rate of new cases as New Zealand despite a much more relaxed lockdown, with many businesses remaining open.

SUPPLIED Dr David Skegg, author of The Health of the People.

Skegg cautioned reading too much into this, saying the Australian situation was a "bit of an enigma" and they had much worse hospitalisation rates than New Zealand, suggesting there was more of the virus in the community than was showing up in tests.

"If you look at hospitalisations, Australia has got 378 people in hospital with Covid-19. We have 15."

He said even after adjusting for population Australia had five times as many people in hospital.

New Zealand was also being more ambitious than Australia, Skegg said, aiming for a low enough case rate that lockdown can be finished after a single month, instead of the many months expected in Australia.

Prime Minister Jacinda Ardern said she agreed with Skegg that New Zealand's contact tracing had to be "second-to-none" and it would be ramped up.

Earlier in the select committee Health Director General Ashley Bloomfield had been unable to say exactly how fast all contact-tracing for each case could be carried out.

The Government has asked Dr. Ayesha Verrall to review its contact-tracing practices.