Ardern said unlike Auckland's hard boundary which will stay in place, the Hamilton boundary will be maintained by spot checks for practical reasons because there are too many feeder roads into the Hamilton area.
She asked people to comply with restrictions and to work from home if they can.
She said the unvaccinated are the "vast majority" of cases because "the vaccine works".
"But it is also because the virus is literally finding unvaccinated people. The vaccine makes a difference, it keeps people safe. It also gives us choices."
Ardern said if the vaccination rate had been at 90 per cent or above in Hamilton or Raglan, it was unlikely that level 3 restrictions would have been imposed today.
"We would be able to rely on contact tracing ... but while we are still vaccinating we have fewer choices."
"Please get vaccinated today if you want to avoid level 3 in your community."
