New Zealand's alert level 4 lockdown might be extended another five days until after the Anzac Day long weekend, a top business leader concedes.

Any delay would also give health officials more time to get contact-tracing up to "gold standard".

Cabinet will meet today at 10.30am, with a public announcement due at 4pm as to whether New Zealand drops to alert level 3 - and more flexibility for businesses - from 11.59pm on Wednesday.

Failing to exit level 4 would be a "real blow" for business, said Employers and Manufacturers Association chief executive Brett O'Riley, and many firms would need direct financial assistance.

"Possibly they might extend the period of level 4 through to early next week, until after Anzac Day, just to give people more time to get up and going,' he told Newstalk ZB's Mike Hosking.

Although Anzac Day falls on Saturday this year, it is recognised as a public holiday on Monday - and the Government will undoubtedly be thinking about how people will react to an easing of restrictions before a long weekend.

Business was seeking certainty and consistency, said O'Riley.

He said manufacturers that probably should have been able to operate at level 4 had exports and supply chains waiting. Australian competitors had been able to continue working and "that's not good".

Meanwhile, the country's top health official has conceded that a key measure in determining whether New Zealand should come out of lockdown is a week shy of being "gold standard".

Director-General of Health Ashley Bloomfield revealed that work was continuing "at pace" to improve contact-tracing, even though Cabinet needs robust information for its decision today about whether to ease or extend the four-week nationwide lockdown.

But Prime Minister Jacinda Ardern said the work didn't necessarily consign New Zealand to the fate of an extended lockdown.

"Don't read into anything," she said when asked about the possibility of a longer lockdown due to the ongoing work on the national contact-tracing system.

Contact-tracing, however, remained one of the crucial factors she listed among the key criteria for today's decision, which will be revealed at 4pm.

Other public health criteria for the decision include the level of community transmission - where the origin of infection is unclear - the amount of testing, border restrictions and the capacity of the health system, including ongoing access to personal protective equipment.

Other key factors Ardern identified were the impact on the economy, the public attitude including people's and businesses' willingness to comply with alert levels, and the Government's ability to work out, communicate and enforce those restrictions.

New Zealand's decision comes as other countries struggle to contain the virus - the number of cases globally is now almost 2.4 million, with more than 163,000 deaths.

Britain will still be in lockdown for at least four weeks, after another 596 deaths in the most recent 24-hour period. There have now been more than 16,000 deaths in the UK.

The US is the worst affected country, with more than 732,000 cases, and more than 38,000 deaths. The US has more than half a million more cases of coronavirus than other hard-hit nations including Spain and Italy, which have just over 191,000 and 175,000 cases respectively.

Back in New Zealand, Auckland University epidemiologist Professor Rod Jackson estimates there are 500 undetected but infectious cases of Covid-19 in New Zealand, which he says is reason enough to extend level 4 because physical distancing was the best way to manage them.

The lockdown is due to end at midnight on Wednesday, but Ardern has warned that level 3, whenever it kicks in, will still be based on the principle of "stay home, save lives".

The number of new cases continued to drop yesterday, a pattern that started 15 days ago.

Nine new cases brought the total to 1431, and with 912 people now recovered, the number of active cases is 507.

The death toll rose to 12 after it was confirmed that the death of an Invercargill man linked to the Bluff wedding cluster was due to Covid-19.

The Bluff cluster is one of 16 clusters and has been connected to more than 90 cases, including the death of the groom's father.

There are 18 people in hospital, including one each in ICU at Middlemore, Dunedin and North Shore hospitals; two are in a critical condition.

Bloomfield said there were six recent cases where the source of infection was unknown - including one in Whanganui and one in Timaru - and targeted testing has been done in Timaru to check for undetected chains of transmission.

Testing had been ramped up in Whanganui in recent weeks due to low per-capita testing in the region, and Bloomfield said more was being considered in light of the recent case there.

Director-General of Health Dr Ashley Bloomfield says he is confident the Health Ministry's contact-tracing would be "gold standard" with a week. Photo / Pool

Hundreds of random tests in Auckland, Canterbury, Queenstown and Waikato in recent days had not returned any positive cases, which Bloomfield said was an encouraging sign that widespread community transmission was unlikely.

Wider targeted testing was vital before Cabinet can make an informed decision, according to epidemiologist Sir David Skegg, who also questioned last week whether the Health Ministry's contact-tracing capacity was up to scratch.

Without confidence in both of those aspects, Skegg said that Cabinet would be playing "Russian roulette" with New Zealanders' health.

Bloomfield has previously said that the ministry was "furiously" working to improve contact-tracing, based on the recommendations of an independent audit - still yet to be released - by infectious diseases specialist Dr Ayesha Verrall.

Yesterday Bloomfield responded to concerns about the ministry's outdated system to manage the Covid-19 data - referred to by one source as a "dinosaur".

There are fears the system cannot work quickly enough to isolate positive cases and stop an outbreak from spreading.

"The system that is being used is not one that's particularly easy to get information out of ... but also to be able to link it to our other health databases," Bloomfield said yesterday.

"That work is happening at pace."

He said the ministry was "on a pathway" to a gold standard contact-tracing system, which was essential "to safely go down to level 3 and lower".

The standard was to be able to trace 80 per cent of all close contacts within three days, and Bloomfield said he was confident that would be achieved "within the next week".

Ardern said it was "hypothetical" to rule out easing the lockdown on the basis of contact-tracing being shy of the gold standard.

But she said New Zealanders could help.

"If I can two pleas to members of the public - if you even have a sniffle or the slightest sore throat, get a test. The sooner we get on top of knowing someone has the symptoms of Covid-19, the more successful our isolation and contact-tracing will be.

"The second thing - think about all your movements as if we may come and interview tomorrow and try and find out who you've been with."

She even suggested that people keep written diaries of their movements and interactions so they could easily find, for example, who they were in close proximity to six days ago.

Professor Rod Jackson said that level 4 should be extended because physical distancing was the best way to manage undetected yet infectious people.

He said there were about 500 such people in New Zealand, based on the infection fatality ratio (the number of deaths per infected people) in countries that had far more cases than New Zealand.

A conservative estimate was that western countries had detected about every second infectious person, so with 507 active known cases in New Zealand, Jackson said there are about 500 undetected but infectious people.

Ardern said that New Zealand was in a position to potentially eliminate Covid-19, but even if the lockdown was lifted after Wednesday, life would not return to pre-Covid days.

In particular she said normal socialising would remain banned because the close interactions of dozens of people could enable a new outbreak.