Just how long the country stays under complete lockdown depends on whether or not more coronavirus cases arise still.

It also depends on people sticking to the rules and staying indoors - and yet another plea is being made to the public to take the current situation seriously.

Director-General of Health Dr Ashley Bloomfield said the planned four weeks of lockdown may well be extended.

"If we've still got isolated outbreaks that we can manage quite easily, then that may allow us to get down to level 3.

"If we're still seeing new cases popping up around the place, then that would give us a sense that we may need to stay in level 4 somewhat longer."

Bloomfield told Mike Hosking this morning that health authorities were now working to figure out what was the criteria - not just the number of cases - and nature of transmission.

They were also looking at how the alert level 4 lockdown would impact the number of hospitalisations and the potential number of deaths related to Covid-19.

It was still too early to identify a trend of those at this stage, he said.

DECLINE IN CASE NUMBERS NOT EXPECTED FOR 10 DAYS

"That's what we're most interested in is to see what the impact is of the actions we're currently taking.

"We're expecting that to keep climbing for a bit and we didn't feel it would be before 10 days. So it will take at least 10 days before we're likely to see a decline."

Again, he emphasised that any decline in the number of confirmed or probable cases identified in New Zealand was dependent on the extent to which the public complied to rules to self-isolate.

"If things go well, we should start to see after 10 days or so that the numbers of new cases each day decline. Obviously our aim is to get right down and effectively break that chain of transmission.

"If you combine that with the border measures - where we can control who's coming in and out - that should really put us in a good position with a very small number of cases."

The ideal aim was to get that figure down to zero, he said.

FIRST COVID-19 DEATH IN NZ

But not even China - which continues to show a marked improvement since the crisis began - has done that, he said.

Bloomfield acknowledged the death of the first person to die from the disease in New Zealand - Anne Guenole.

Guenole, in her 70s, died yesterday morning at Grey Base Hospital in Greymouth after testing positive for Covid-19 on Friday. It was earlier thought she had a strain of the flu.

Covid19.govt.nz: The Government's official Covid-19 advisory website

Her family is now working to figure out how she became infected. It is understood she had an underlying health condition that may have contributed to her death.

Bloomfield said the public needed to remember it was not just older people who could come down with the virus.

"It's not just older people and people with pre-existing conditions. Yes, they are more likely to die. However, it can affect other people - even young people can die from this.

"People with pre-existing conditions and older people - it tends to be if they get an infection like this or even influenza or some other infections, because they have less ability to fight it off, then they tend to get the complications that then lead to death.

"So it's a contributing factor and it's an important contributing factor."

New Zealand has a total of 514 confirmed or probable cases of coronavirus as of the latest update.