Motorways were clogged overnight as Aucklanders rushed to supermarkets and some routes were closed for roadwork maintenance.
State Highway 1 was closed at multiple points for scheduled maintenance, with lengthy queues along the motorway.
A picture snapped by a motorist stuck in traffic on the Southern Motorway at Newmarket showed substantial queues in the city, as cars followed set detours.
The arterial route was closed for scheduled roadworks just as the Prime Minister made the announcement Auckland would be moving to alert level 3.
It came after four cases of Covid-19 from the same family were confirmed - after 102 days without any cases of community transmission.
Ardern and director general of health Ashley Bloomfield announced the news last night and an alert was sent to New Zealanders' phones.
As of noon today, Auckland will move to level 3 for three days until midnight on Friday.
The rest of the country will move to alert level 2 at midday - until midnight on Friday.
People in Auckland who need to go home to another region can do so but they should keep an eye on their health, Ardern said.
"We're asking people in Auckland to stay home to stop the spread," Ardern said.
More advice will be made available today for these people and those who have recently travelled from Auckland.
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There were chaotic scenes at Auckland supermarkets following the announcement, as shoppers ignored pleas against panic-buying.
Simon Oosterman told Newstalk ZB the line of eager shoppers stretched 2km from the Countdown New Lynn supermarket.
"I counted over 200 people in the line, there are cars literally queuing up outside because there aren't enough car parks."
Oosterman had been standing outside the supermarket for the past half hour and the queue hadn't yet budged, he said.
Physical distancing measures will be introduced to Countdown stores throughout the country in response to alert level 3 measures in Auckland and level 2 measures throughout the rest of the country.
There will also be limits on customer numbers, limits on some products, queue control and extra cleaning and hygiene measures, Countdown said on its Facebook page.
"We're well practised in what needs to be done to keep our team and customers safe, and there's plenty of food and supplies for everyone," the supermarket said.
"Please keep shopping as you normally would and there is no need to stock up. Look out for each other, and stay safe."