Confirmed measles cases in Auckland have now reached 778.

Auckland Regional Public Health Service, medical officer of health, Dr William Rainger confirmed on Saturday 19 new cases over the past 24 hours.

Children under the age of 5, and those aged between 15-29, were most affected. Forty per cent of people who had contracted the illness had needed hospital treatment.

"Some of these people have been very very unwell," Rainger said.

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He said the priorities for health officials were to limit measles' spread in Auckland, protect the most vulnerable, increase the uptake of vaccinations and also limit the spread across the country.

Advice was also being sent to schools on how to prevent the spread elsewhere in New Zealand.

While officials did not want public events to be cancelled, people who were feeling unwell have been told to "stay away from events".

"People who think they have measles should also stay away from events," he said.

Rainger added: "The risk to most people out and about is still very small. But also if there is a case it spreads very easily. One measle can spread to 15 other people . . . the flue is more like one infected person can pass it on to two people."

The latest outbreak is not the worst in total, but is the biggest in recent years.

In 2014, 114 cases were reported, and three years earlier an outbreak saw about 500 cases.

A national outbreak in 1997 saw several thousand people contract measles.

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Rainger said he couldn't predict when the latest outbreak would be under control.

His advice was for people to make sure they were immunised.

"I think there can be done degree of confidence that it can be stopped from spreading to the rest of the country."

While the Auckland outbreak had now topped 700, he said that had to be kept in context of the region's population of 1.6 million.

"So it's not a crisis. It's serious outbreak of a serious disease and people should get immunised."

A series of pop-up vaccinations were held in South Auckland today. The clinics – in Manurewa, Mangere and Manukau – will continue today.

More than 120 people received vaccines today.Carmel Ellis from Counties Manukau DHB said the day had been "a learning experience for pop up clinics. Will have more nurses on tomorrow."