Gatherings of more than 500 people should be cancelled to help stop the spread of coronavirus, Prime Minister Jacinda Ardern says.

Within the next month, she said there were 107 events expecting more than 1000 attendees were expecting to take place in New Zealand's major centres - but the Government had to protect the public from Covid-19.

"To slow the spread and reduce the number of people infected ... Cabinet agreed that gatherings of 500 or more people held outdoors or indoors should be cancelled."

This applied to non-essential events including sporting and religious events, but excluded school or university events.

Today's announcement would give certainty to event organisers, but further guidance on public gatherings would be announced further in the week, she said.

"Ultimately I know this decision is hugely disappointing. I know it will have an impact on a number of communities ... but we are making this decision in the best interest of New Zealanders."

The Government was not shutting schools or universities because "that is not where New Zealand is at".

Zero tolerance for those refusing to self-isolate

She said there would be "zero-tolerance" for travelers who did not self-isolate.

Ministers would use the Immigration Act to deport people on visitors visas, and deportation was a serious blight on someone's record.

Anyone refusing to self-isolate was "not welcome" in New Zealand, she said.

Ardern also confirmed that she would not attend the Asean trip to Vietnam scheduled for April.

Economic response

Ardern said the first phase of the Government's coronavirus response, to be announced tomorrow, would focus on keeping Kiwis in work.

A mass public awareness campaign to unite against Covid-19 would be launched on Wednesday, she said in her weekly post-Cabinet press conference.

She said most Kiwis were able to go to work today, but in Italy or Spain that is not the case, countries whose economies are essentially shutting down.

That emphasised the importance of New Zealand's new travel restrictions, she said.

Slowing the transmission of Covid-19 was the best way to secure the economy in the long run, she said.

"We are working around the clock to ensure our economic package will focus relentlessly on jobs."

It would also give the health system the resources it needs.

She said preliminary advice from Treasury this weekend was that the impact could be greater than the impact of the GFC.

"There is no existing playbook for the economic response here."

The Government was prepared for "this rainy day".

It comes after the Reserve Bank of New Zealand delivered a shock 0.75 per cent cut to the official cash rate (OCR) this morning, citing Covid-19 as the reason.

It now sits at 0.25 per cent – the lowest it has ever been.

In welcoming the Reserve Bank's news, Finance Minister Grant Robertson said the Government's "multi-billion dollar package" would help stimulate the economy and help Covid-19 hit businesses.

"Government surpluses and low debt put us in good shape to invest in the economy to support businesses and workers."