New Zealand Prime Minister Jacinda Ardern has pointed the finger at Australia as her country’s Delta outbreak expanded on Wednesday.

The outbreak jumped from one to seven people as New Zealand began its first nationwide lockdown since May last year.

The level four lockdown – with NZ’s harshest level of restrictions – will last at least three days in an attempt to quash the spread of the deadly virus.

Genomic sequencing confirmed the strain as the Delta variant, and a link to the NSW outbreak.

“That means level four was the right decision,” Ms Ardern said.

“Our case has originated in Australia. Our job now is to work through how and when it got here.

“There is more work to be done to help piece together this puzzle … a lot of leads to chase down.”

Under the lockdown imposed at midnight on Tuesday, Auckland and the Coromandel, where ‘Case A’ travelled while infectious, will spend at least seven days in lockdown.

After being challenged for locking down the whole country with just a lone case on Tuesday, Ms Ardern was quizzed on the move again on Wednesday. Her response was brief.

“What is your message to people who question the need for an alert level 4 lockdown?” a journalist asked.

The PM pointed west.

“Australia,” she said.

Just how the virus got from NSW to New Zealand is still to be determined. There are at least three people in hotel quarantine in New Zealand with the virus who have travelled from Sydney.

The escalation of NZ’s outbreak came as NSW’s own virus crisis exploded, with 633 more local infections reported on Wednesday.

Only 94 of them were in isolation throughout their infectious period.

Wednesday’s shocking tally, which also included three more COVID-related deaths, easily topped the previous daily high in NSW of 478 cases reported on Monday.

Premier Gladys Berejiklian revealed that every person in NSW with the virus was still passing it on multiple times.

“According to the data we have every person who has the virus is spreading it to at least more than one person,” she said.

“What the data is telling us in the last few days is that we haven’t seen the worst of it.”

Ms Berejiklian rejected suggestions that harsher restrictions akin to those in Melbourne or New Zealand were needed, saying the lockdown was appropriate and extremely strict.

She maintained a lack of compliance was the issue.

“In one day alone, more than 400 people police know of across the state … left their house for the wrong reason,” she said.

“You can have the strictest rules in place … Delta leaves no room for anybody doing the wrong thing.”

South-west and western Sydney remain the highest for transmissions with 440 of the recent cases occurring in those areas.

“I can’t express enough my level of concern at these rising numbers of cases,” chief health officer Kerry Chant said.

“Shop local, stay local, and spend the least time in a place where there are other people that you can.”

Dr Chant said vaccination rates were still far too low and there were 462 COVID patients in hospital, with 77 in intensive care and 25 on ventilators.

Wellington’s streets were empty as NZ began its three-day lockdown on Wednesday.

Back across the Tasman

New Zealand’s director general of health Ashley Bloomfield said generic modelling suggested Auckland’s new Delta cluster could grow to about “50 and 120 cases”.

In a pattern that is also becoming more common in Australia, six of the seven cases are young people who have socialised heavily while thought to be infectious – including trips to a nightclub, church and the casino.

“We’re expecting more [cases]. Particularly of the age group and demographic,” Ms Ardern said.

Case A is a 58-year-old man who lives in Devonport, an affluent coastal suburb in North Auckland, a tradesperson who visited several homes while infectious.

Others are his co-worker, a 21-year-old female health worker at Auckland Hospital and a 25-year-old woman who teaches at Avondale College.

The hospital is in “a form of internal lockdown” according to Ms Ardern, who downplayed the risk to the country’s under-resourced health system.

“We’ve had COVID-positive cases in our health workforce before … they’re well versed in these practices,” Ms Ardern said.

The cases are New Zealand’s first in the community since February, a 170-day streak that officials warned would likely end at some point.

Under the lockdown rules, Kiwis must stay within their household “bubble” and leave the house only for a handful of essential reasons.

Travel is severely limited, schools are closed, and only essential businesses – such as supermarkets, petrol stations and pharmacies, where people must wear masks – are closed.

Holidayers have been given 48 hours to get back to their normal place of residence, sparking a frenzy on domestic Air New Zealand flights.

-with AAP