Measles is one of the most infectious airborne diseases.
New Zealand's secondary schools rugby league competition, due to be played next week, has been cancelled amid the current measles outbreak.
In Auckland, more than 750 cases of measles had been confirmed as of midday today. The tournament was to be held in Takanini.
New Zealand Rugby League scrapped thetournament after seeking medical advice, chief executive Greg Peters said.
"We understand people may be disappointed by our decision and we apologise for any inconvenience caused; however, the welfare of our players and all involved in the tournament comes first."
Held at Pulman Park between Monday and Friday next week, 26 schools from across the country were set to take part in the tournament.
It was not appropriate for the tournament to go ahead because the vaccination status of the participants was uncertain, NZRL medical advisory head Dr John Mayhew said.
The outbreak, which started in January, had swept the nation with Counties Manukau the hardest hit with at least 500 confirmed cases.
Ardern, who said her own baby Neve was up to date with her vaccinations, said she was worried about those who choose not to get immunised.
The public was told they should stay home if they are unwell with the symptoms of measles, an Auckland Regional Public Health Service spokesperson said.
"The service is not advising that people stay away from events or that these be cancelled.
"People should, however, remain at home if they have been told to be in quarantine, even if they are feeling well.
"With the measles virus circulating around Auckland, people can catch the virus in any public space or from people they know."
People aged 50 or over are considered to be immune to measles. Everyone else aged over 12 should be immunised with at least one MMR vaccination.
