Auckland's public health service has stopped tracking people exposed to measles because there are now so many.
And some doctors are calling for a national mass vaccination to control the spreading outbreak.
The central Auckland and Waitemata health districts have been worst affected in an outbreak since May. By last week, 250 cases had been reported.
Waikato has been affected since July, with more than 20 cases and many other areas have had sporadic cases of the highly infectious viral disease.
Of the 29 new cases of confirmed or probable measles reported last week, 19 were from the Auckland region. The remainder were in six other health districts from Northland to Southland.
"There has to be a serious look at the control of the current outbreak," said paediatric infectious diseases specialist Professor Diana Lennon, of Auckland University.
"The main option is to do a mass campaign, to consider vaccinating everybody from one year of age to the end of school.
"We've got to mop up the years and years and years of poor vaccine delivery."
The director of the Immunisation Advisory Centre at Auckland University, Dr Nikki Turner, agreed on the need for catch-up work to fill in the gaps in the national coverage with measles, mumps and rubella (MMR) vaccination.
She said although New Zealand now had reasonably high coverage of young children - 90 per cent of 2-year-olds were up-to-date with their immunisations - there were big gaps among older children and young adults.
"So throughout New Zealand we've got pockets of people who are not immunised, who can transmit measles."
"A lot of people still have this myth that measles is a disease of young children, but we're seeing measles in adults, young adults, older adults, older kids."
The clinical director of primary care at the Auckland and Waitemata District Health Boards, Stuart Jenkins, said the regional public health service had ceased tracing measles cases because the boards had decided it was now better to increase vaccination.
Under what the DHBs call an "enhanced immunisation programme", they urge everyone born in 1969 or later who hasn't been vaccinated - or who isn't sure - to talk to a GP about receiving the state-funded MMR vaccination.
People born before 1969 are expected to have been exposed to measles and are considered immune.
Asked if a national mass campaign to fill in the vaccination gaps was being considered, a Ministry of Health official said the ministry already funded vaccination of those born in 1969 or later.
"For the past few months, the ministry ... has been encouraging general practitioners to increase measles immunisation as much as they are able to ... ," said deputy public health director Dr Darren Hunt.
The ministry's Immunisation Handbook recommends children be given two shots of MMR, generally at 15 months and 4 years of age, although the first can be given earlier and the second a month later.
* 358 cases reported nationally this year.
* 250 cases in Auckland region since May.
* 64 cases nationally have needed hospital treatment this year.