Day one of Auckland's lockdown to try and prevent the spread of Covid-19.

New Zealand's total number of coronavirus cases has jumped to 283, as the country begins a four-week lockdown to break transmission of the virus.

Overnight, strict quarantine measures for Kiwis returning from abroad came into force. Eight have been quarantined for having possible symptoms of the virus, and 160 have been held until they can organise an appropriate method of travel home.

Director-General of Health Dr Ashley Bloomfield, during a Thursday press conference, said health officials had identified 78 new cases of Covid-19, including 73 confirmed and 5 probable cases.

KEVIN STENT/STUFF "The majority of New Zealanders are already ahead of that compliance," Police Commissioner Mike Bush said. (file photo)

Seven people were in hospital, and 27 had recovered from the virus. The majority of the new cases appeared to have links to overseas, and further clusters of the virus and community transmission were being investigated.

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A total of 12,683 tests had now been run. Bloomfield said health officials could not test every person coming through the border, because this would exhaust the country's daily testing capacity.

It could take ten days of strict lockdown to see a decline in the climbing coronavirus numbers, he said.

"These are unprecedented times for this country, and indeed people around the globe ... We would expect the number of Covid-19 cases to increase in the coming days," he said.

Prime Minister Jacinda Ardern on Wednesday, when 50 new cases were announced, said New Zealand could expect to have "several thousand" confirmed cases of Covid-19.

Ardern earlier in the week announced New Zealand would enter a month-long lock down to combat the virus.

As of Thursday, only essential workers would be able to leave their homes, and all non-essential businesses and schools would be shut.

Police Commissioner Mike Bush, also at the Thursday press conference, said officers had already come across people who claimed not to know about the lockdown.

"The majority of New Zealanders are already ahead of that compliance," he said.

Police will initially take a discretionary approach, he said.

On the quarantine of returning Kiwis, Bush said everyone who had arrived on Thursday morning had been greeted and questioned by Customs officials.

A total of 360 people had come through the border, and eight had been put into quarantine in hotel rooms.

There were 160 people with insufficient plans to return home in self-isolation. They had also been placed in hotel rooms until they could make sufficient plans. Returning Kiwis are now expected to be able to travel from the airport into self-isolation, alone.

Bush said returning Kiwis could be collected by one person who would be in their "bubble" for the month-long lockdown.