Prime Minister Jacinda Ardern has defended her Government's extension of the Auckland lockdown to protect people's health, as the business sector warns of closures and job losses.

Ardern's comments come as the National Party say they and the public are being left in the dark over specific health information that formed the basis for the lockdown extension.

The hospitality sector say many bars and restaurants won't reopen as they struggle to cope with the four-day extension to the Auckland level-3 lockdown.

A reprieve from level 3 won't come for Aucklanders until 11.59pm Sunday, and they will then have to wait another week before they can have social gatherings of more than 10 people.

Ardern said more time was needed at alert level 3 to have greater confidence about the perimeter of the current outbreak, which now includes New Zealand's largest cluster.

"It's all on Covid," Ardern told Newstalk ZB's Mike Hosking today, when he asked if it was fair to suggest the extended lockdown was all on her and the Government.

"When I look around the world, every other country is having similar experiences, battling Covid or dealing with a resurgence. We are not alone in that."

Asked whether decision-making needed to be more apolitical, she said the independent health advice was comprehensive. "We have the job of making sure we constantly weigh up the economic impact. Our view is a strong scientific, health view is the best way to support our economy."

When asked by Hosking whether the border had leaked, she said authorities were still hunting what had caused the Auckland cluster outbreak, including comprehensive testing of people at the border.