Roadblocks will be set up around Auckland, preventing non-essential travel from the region for the next three days.
Yesterday, people were able to drive in and out of the nation's biggest city freely, but today that has changed.
It comes after Auckland headed back into Covid-19 Alert Level 3 and the rest of the country into Level 2 at midnight.
Prime Minister Jacinda Ardern made the announcement following three new community cases in South Auckland. The cases have the new UK variant and are not linked to any previous managed isolation and quarantine cases.
Police are at eight checkpoints in and out of Auckland, questioning people over if their travel is essential.
Anyone whose travel is not essential will be turned away.
An officer in Mercer told 1 NEWS there had been a lot of people trying their luck this morning, with about one in four cars being turned back where they came from.
People who need an exemption are advised to go to the Ministry of Business, Innovation and Employment website.
Businesses in Auckland can register for travel documents using an online register, which allows businesses to request and receive travel documents for workers who need to cross an alert level boundary.
"The document can then be used at checkpoints, making passage much quicker and simpler for both workers and police," MBIE said in a statement this morning.
Aucklanders trying to return home can do so, as well as those in Auckland trying to return home to elsewhere in the country.