Prime Minister Jacinda Ardern addresses ongoing measles outbreak

There have now been 963 cases of measles confirmed across the country, Prime Minister Jacinda Ardern says.

Auckland remains the only centre with an official outbreak declared, and particularly South Auckland.

Ardern said the Ministry of Health had been training 25 new nurses to help with vaccinations and considering letting pharmacists provide MMR vaccines.

She said New Zealand was far from unique, with outbreaks currently occurring a number of other countries.

The country is grappling with the worst measles outbreak in more than two decades with the Auckland Regional Public Health Service on Monday confirming there had now been 804 cases in the region alone.

Ardern reiterated calls for people to take up free immunisations and stay at home if they had symptoms.

Asked whether Auckland health officials had moved too slow, Ministry of Health's Director-General Ashley Bloomfield said there had been "good information" provided to the public.

He said decisions about whether specific events events went ahead fell with organisers.

Looking outside of Auckland, Bloomfield said low vaccination rates in Northland were also a concern.

Bloomfield said evidence suggested shortfall in vaccination rates was related to hesitancy and lack of access, rather than direct opposition to vaccines or "anti-vaxxers".

Bloomfield said previous evidence suggested less than 5 per cent of people in the '90s had actively opposed vaccination, despite anti-vax lobbying.

"We're expecting to keep going up another week or two," he said, adding it was expected to peak about then.

He said it would only be declared an epidemic if there were outbreaks in other parts of the country.

Last week, the Government deployed the National Health Coordination Centre (the NHCC) to organise the response to the outbreak, associate health minister Julie Anne Genter calling it a top priority.

Ardern is on Monday afternoon set to provide an update on the nationwide push to improve vaccinations and slow the spread as she holds her weekly press conference.

She's being joined by the Ministry of Health's Director-General Ashley Bloomfield.

In Auckland, about 50 schools and a similar number of early childhood centres have had confirmed cases this year with hundreds more pupils potentially exposed after an infected student went to the St Peter's College school ball over the weekend.

Most of those affected are aged 20 to 29 years and the number of cases has been growing at about 18 or 19 a day.

It is the largest outbreak since the 1990s by a significant margin and comes amid falling vaccination rates since 2015.

The Government last week announced it was opening outreach centres in South Auckland – a major centre of the outbreak - to allow more people to get free vaccinations.

"People under the age of 50, especially children, who have not been vaccinated, should seek a free vaccination from their doctor as soon as possible," Genter said.

Meanwhile, pharmacists and the Opposition have also been calling for the Government to change rules to allow chemists to administer the measles vaccine.

There are 864 pharmacists around the country who are allowed to give vaccinations for the flu, shingles, whooping cough and meningitis, but current rules mean they don't get funded to provide the MMR (measles, mumps, rubella) vaccine.

The Pharmaceutical Society of New Zealand says its members could play a role in helping improve vaccination rates.