There has been a big spike in Auckland's measles outbreak, with 126 new cases in the last eight days.
The big rise in infections takes the year's total to 509 and made last week the worst since the outbreak started.
The majority of Auckland cases - 288, or 57 per cent - have been in South Auckland, putting huge strain on Middlemore Hospital, which has opened a dedicated measles ward.
A leading immunisation expert now wants more Government funding to halt the disease.
Associate Health Minister Julie Anne Genter would not commit to that yesterday, but said she had asked for urgent advice from her ministry on what else can be done to improve vaccination rates.
"The measles outbreak is extremely concerning, and I am keeping a close eye on what is happening," she told the Herald.
"We need to continue to find ways to deliver services to meet the needs of families, such as ensuring immunisation services are available in more accessible places and times."
Papakura Marae Health Centre clinical director Dr Rawiri Jansen, who treated one of the first patients in the outbreak six weeks ago, said poverty and transience in South Auckland made it difficult to stamp out measles.
His clinic sent a 21-month-old boy to Middlemore Hospital's emergency department after he contracted measles from a childcare centre and developed pneumonia.
The family's poverty and lack of a permanent address made his treatment more difficult, Jansen said. It meant the boy's mother had earlier focused on day-to-day priorities rather than keeping her son's immunisation up to date and hindered follow-up treatment and efforts to contain the disease.
The baby boy's infection also highlighted the strain measles put on the health system. The clinic had to send its other patients home in the middle of the busy winter season and then do a major scrub and disinfection of every room. It then set up a dedicated isolation room to handle other patients coming from the childcare centre with measles.
Counties Manukau Health's general manager of child, youth and maternity Carmel Ellis said it was working closely with other health agencies to contain the disease now there were 300 confirmed cases in its district.
The district health board's Kidz First children's hospital was currently treating two children for measles and had treated a further 137 patients since the outbreak began.
It had set up an isolation ward with 12 beds as part of its "standard protocol" for airborne diseases.
The health board was also stepping up efforts to promote vaccination.
The 639 cases nationwide this year have now exceeded the last significant outbreak in 2011, when there were 597 cases across the country. Of this year's total, 237 were so sick they required hospitalisation.
Dr Nikki Turner, GP and director of the Immunisation Advisory Centre (Imac) at the University of Auckland, said the "huge numbers" were "heartbreaking".
"It's really simple - if we vaccinate enough people we don't see measles."
The outbreak was placing a huge burden on Middlemore and Starship in the middle of winter, on top of the usual winter demand, she said.
Big international outbreaks were further increasing the likelihood of measles entering New Zealand, while the country's formerly poor immunisation rates meant a large number of teens and young adults were unaware they were at risk.
In addition, severe poverty was getting worse.
"For families living in severe poverty, the challenges of preventive healthcare are way down the priority list," Turner said.
Hospitals were also full of vulnerable people susceptible to contracting measles.
This month the Herald revealed the World Health Organisation (WHO) was likely to pull New Zealand's "elimination" status if the measles outbreak was not curbed by March next year.
"The only way [to halt this] is to put more effort into finding people, reminding them and offering them the vaccine, and raising awareness of the urgency of vaccinating," Turner said.