With the Government assuming the majority of those infected would have links to overseas travel – and therefore focusing its testing on them - it was hard to gauge the true extent of community transmission, he said.

"The actual number of people who have been infected will be far higher than the 589 notified and we really have no idea of the extent of community spread," said Sir David.

"I'm afraid that only complacency can have allowed our authorities to imply that the virus would behave differently here than everywhere else."

Suppressing the virus was only the first step in eradicating it, he said, adding that it was "worrying" the Government wasn't clearly talking about eliminating it completely.

"A lockdown on its own is not enough. It's like pressing the pause button on your device."

Tackling a virus of this kind took a willingness to be transparent and change tactics when necessary, he said.

"If elimination cannot be achieved, when and how will we know that? And what will be the next goal? Those are the kinds of things I would expect to see in a strategy document".

Minister of Health Dr David Clark, told the committee that the Government's current plan was informed by modelling it had seen which said the country could see 14,000 deaths if no significant action was taken.

Both the border closure and the lockdown was a preventive measure to stop such a "totally unacceptable" situation, Dr Clark said.

He admitted that the country still faces a uphill battle.

He said intensive measures may need to be in place for some times, but that wouldn't necessarily mean the whole country would remain in lockdown.

The country raised its alert level to 4 – the highest level – on Thursday. All non-essential businesses were forced to close and all Kiwis required to self-isolate. People are only allowed to leave their house to exercise or to visit the supermarket or pharmacy.

The lockdown will last at least four weeks.

Globally, there have been more than 775,000 confirmed cases of COVID-19, with the death toll standing at more than 37,000.

One person so far has died in New Zealand due to the disease.