The new directive currently excludes schools and universities.
Ardern said there were more than 100 events of this size set to happen in the coming weeks.
She said there will be further guidance issued later in the week giving a clear pathway to help organisers of smaller events determine whether they need to cancel.
Turning to border issues, the prime minister said there would be zero tolerance for those who don’t follow rules of self-isolation, with holders of visitors visas being liable for detention and deportation.
Ardern said if anyone comes to New Zealand and has no intention of self-isolating, “frankly you are not welcome”.
The prime minister also said preliminary Treasury advice was that the economic impact of the novel coronavirus could be greater than the Global Financial Crisis.
It comes amid news Air New Zealand could cut its workforce by up to 3750, according to the New Zealand Air Line Pilots’ Association (NZALPA).
President Andrew Ridling met with Air New Zealand senior management on Monday, and released a statement after discussing reductions on both international and domestic routes due to the effects of COVID-19.
“The industry is aware that, until this unprecedented situation developed, Air New Zealand would have had forecasted annual revenue of approximately $NZ 6 billion dollars. I would no longer be surprised if that forecast is reduced to around $NZ 1 billion,” said the statement.
“The company have now advised NZALPA that, based on current modelling, Air New Zealand will be looking to reduce employee headcount across the organisation by up to 30 per cent. We understand this will not be a short term measure.”
