The government is tightening its rules for mask use under the 'red' traffic light setting.

Prime Minister Jacinda Ardern says under the red setting, masks must now be worn at food and drink businesses, close proximity businesses, events and gatherings.

The same exceptions for when people are eating, drinking or exercising still apply.

She says the changes do not apply to non-public facing workplaces, swimming pools, and gatherings where people have the exclusive use of the premises.

Face coverings must now also be "an actual mask", the prime minister said during her post-Cabinet briefing.

"That means no more scarves, bandanas, or as some of us may have seen from time to time, t-shirts pulled up over the face, for example."

All workers legally mandated to be vaccinated must also now wear a medical-grade mask, for example type 2R or level 2 mask or above, while working in public-facing roles. This includes the widely available blue medical grade disposable masks.

Director-General of Health Dr Ashley Bloomfield, who also attended the briefing, says the government is not recommending the use of N95 masks for the general public.

This is partly because they are expensive and may not be easy to access for some people.

He says for the general public, a three-layer cloth mask is acceptable.

Ardern says this guidance rather than a rule.

School students Year 4 and up are already required to wear a mask. For consistency they will now need to wear a mask while on Ministry of Education-funded school transport services and public transport.

Ardern says the science has been updated and these changes will help save lives and give time to get more of the population boosted.

The Ministry of Health will be updating guidance on masks, including how to safely reuse masks that can be reused, and how to ensure the best fit.

Covid Response Minister Chris Hipkins has defended the recommendation that people use disposable surgical or medical grade masks, saying it is an issue of practicality.

"We are using in N95 masks in those higher risk settings, such as healthcare workers, those who are working at the border," he told Checkpoint.

"We've got to make sure that people can comply and we know that those paper masks - the medical grade masks - they're readily available from the supermarket ... so people can actually use them."

Hipkins says he will have more to say soon on mask supply and mask use in schools.

"We're also making sure we're working with community organisations, food banks and others to make sure that masks are available to those who might not otherwise be able to access them."

-RNZ.