Extending the North Waikato level 3 border is necessary to help protect those most at risk, Waipa's mayor says.

Waipā district will join Ōtorohanga and Waitomo districts in level 3 from 11.59pm today.

Covid Minister Chris Hipkins announced the widening of the border at this afternoon's press conference, while also revealing there were five new cases in the Waikato outbreak.

Asked why the boundary wasn't extended yesterday, Hipkins said there wasn't time to do it yesterday and the decision was ultimately made "out of an abundance of caution".

However, the evidence suggested the outbreak was still relatively contained.

Hipkins highlighted Te Awamutu as being a location where there had been lots of travel between areas linked to Covid cases but he didn't believe the delay in making today's boundary decision contributed to further transmission.

There were still only two cases outside the current Waikato alert level 3 area; Kawhia and Karapiro.

Waipa Mayor Jim Mylchreest said yesterday he was worried the virus was slowly seeping out of the North Waikato boundary, with the announcement of the two cases, and how it would be contained.

Altering the boundary would be "really challenging" as he knew the impact levels 3 and 4 had on businesses, however he was subjected to public "vitriol" after suggesting it might have to include the whole North Island given the number of roads which radiate around the Waikato.

However, he welcomed today's decision and said it had to be done but hoped now more residents would go out and get vaccinated.

"We need the vaccination numbers to skyrocket so we don't need to step in and out of alert levels over and over again.

"If you haven't been vaccinated, you only need to look at the data. Those who haven't been vaccinated are the vast majority of cases and hospitalisations.

"Those who have been vaccinated have recovered quickly and have had less complications.

"The science is there, just listen to it."

Unlike residents in the neighbouring Otorohanga district - which has the lowest vaccination rate, 32.9 per cent, in the country - Waipa is reasonably high in the stats, with 45.8 per cent of residents being double jabbed.

Kaikoura has the highest rate of 57.5 per cent of residents having both vaccinations, according to a Herald insights investigation.

As well as getting vaccinated, he asked residents to talk with those who were unwilling or unsure about getting vaccinated to help understand and alleviate their concerns.

"We're the home of champions so let's lead the way and get vaccinated, Waipā. Do it for your, children, grandchildren, parents, grandparents and your friends. Do it for New Zealand."

Hipkins said Hamilton Airport would also be included in the boundary extension and any travellers would need a Covid test.

The boundary would be high-trust given the number of roads leading into the area and people are asked to carry proof of why they are travelling if they are stopped by police.