Auckland Mayor Phil Goff says he is disappointed alert level 3 restrictions for the city have been extended by four days.

Prime Minister Jacinda Ardern said this afternoon Auckland would stay in lockdown until 11.59pm on Sunday, and the city and the rest of New Zealand would remain at alert level 2 after that.

The current schedule was for level 3 in Auckland and level 2 for the rest of the country until 11.59pm on Wednesday.

The extra four days would allow Auckland to move down a level "and stay down", Ardern said.

Goff said he was "disappointed", but believed Aucklanders would understand why the decision was made.

"This will be difficult for people whose jobs and businesses are most affected by level 3 restrictions.

"However, the advice given by medical experts is clear; if we ease up on restrictions too early, we risk a further resurgence and losing the benefits we gained from ensuring the virus is contained."

The extension follows calls from the business community to end the restrictions as soon as possible, as the Auckland Chamber of Commerce reports 20 per cent of businesses fear they might not make it through another extended lockdown.

However, Goff said we had seen from cities such as Melbourne how quickly Covid-19 cases could escalate if strong measures were not followed through, and the high death rates and increased economic pain it could cause.

"I want to thank Aucklanders for their patience and sacrifice to date. I know it hasn't been easy, but we need to continue doing what we know works.

"Allowing the virus to gain a foothold in Auckland would risk significant loss of life among some of our most vulnerable communities and would also have severe economic impacts and effects on already struggling businesses.

"We need to stamp out this latest outbreak as quickly as possible so that we are not forced into a worse situation later."

As part of today's announcement, Ardern said everyone would be required to wear masks on public transport for level 2 and above, and this would come into force on Monday.

Goff urged Aucklanders to continue following such guidelines, along with physical distancing, hand washing, and tracking movements with the NZ Covid Tracer app.

"Everything we can do in the fight against this disease makes a difference, and I believe the mandatory wearing of masks on public transport is sensible given our recent experience.

"It is also strongly advised to wear a face covering in other situations where physical distancing is difficult, such as when going shopping.

"Please continue to be vigilant for Covid-19 symptoms — contact your GP or Healthline if you get sick and follow their advice on testing.

"Aucklanders have beaten this virus once by working together. If we all stay the course for the next four days, we will have the best chance of beating it again and getting back to level 2 and level 1 restrictions as soon as possible."