Prime Minister Jacinda Ardern goes on a self-described 'rant' at young people, saying they are the most likely to catch Covid-19 and, though they may not be badly affected by it, will be the ones to pass it on to those more vulnerable.

Prime Minister Jacinda Ardern unleashed on 20-somethings who weren't taking the coronavirus seriously at her daily press conference today.

She said 20-29-year-olds were the most infected with Covid-19 and while they might not be in as much danger as older people, they were currently acting as the main vector for transmission in New Zealand.

20-29 year olds make up 183 of the 702 confirmed and probable cases of Covid-19 in New Zealand, far higher than any other age group.

MONIQUE FORD/STUFF Jacinda Ardern said 20-29 year olds who felt invulnerable were putting the whole country at risk.

The self-described rant from Ardern came after she was asked about compliance with the country's strict lockdown rules, aimed at preventing transmission of the deadly virus.

Ardern said the Government had asked a lot of New Zealanders and most were complying and taking it seriously - but there was a small minority who weren't.

"I think the majority of New Zealanders are doing an amazing job. We just need to keep reminding that small proportion who perhaps aren't taking it seriously why it is so important."

"This period of time is our chance to break the chain of transmission. The quicker we do that the sooner we can return to some semblance of normal life."

She said people had to realise this was not a problem for "someone else" but was about "you and your family".

This was particularly key for young people who were at this point the ones getting infected by Covid-19 the most.

"If I could just point to some of the data at the moment. The most affected age-range by Covid-19 in New Zealand is far and away currently 20-29-year-olds. They are the ones that we are identifying as having Covid-19 in New Zealand."

"They may think that this won't affect them much - that they'll be mild to moderate. They are our vector for transmission. They are the ones that pass it on."

Coronavirus has now killed people at almost every age but has a much higher mortality rate for older people.

Government modelling released on Tuesday suggested that if Covid-19 was not contained almost 9 in 10 of the thousands who died would be 60 or older.

On Wednesday, Director of Public Health, Dr Caroline McElnay announced the combined total of confirmed and probable cases in New Zealand was 708, 61 more than yesterday.

McElnay said the numbers continued to be encouraging but they did not yet signal a turn-around.

Ardern, speaking on the fewer cases being confirmed, said "it is still too early to assess" whether the lockdown measures were successful.