Thousands of extra measles vaccines are on their way to Canterbury amidst an outbreak which has left some clinics running dry.

There are 25 confirmed cases of the disease and huge demand for the measles, mumps and rubella (MMR) vaccination.

Over the next 24 hours, 18,000 extra doses of the vaccine were being transported to Canterbury, with the first batch due to arrive today. They would be available from Wednesday, with more supplied to follow.

Health Minister Dr David Clark said the number of measles cases was expected to rise and people needed to ensure their vaccinations were up to date.

"Vaccination is the best protection against this serious and highly infectious virus that spreads very easily from person to person," Clark said.

"The MMR vaccine is very effective and it's free."

Pharmac, the Canterbury District Health Board (CDHB) and the Ministry of Health were working closely together to ensure there were vaccines available to the people who needed them.

"Children who have not yet been immunised are at the greatest risk from the disease, so it's important to make sure you and your family are up to date with their immunisations," Clark said.

Priority groups for the vaccine were children and young adults (5 to 28 years old) who were not immunised or had only received one MMR dose to date, children 12 months to 5 years who have never received any doses of MMR, and adults aged 29-50 years as this group only received one dose of measles vaccine.

The four-year-old MMR could be brought forward to no sooner than four weeks after the previous MMR.

"Measles is highly contagious and it is in everyone's best interest that people in these priority groups get vaccinated, both to protect themselves and the wider community," Clark said.

"We're also closely monitoring for possible cases in other DHBs."

Normal scheduled immunisations were unaffected, Clark said.

Canterbury Primary Response Group coordinator Dr Phil Schroeder said Canterbury had high levels of vaccinated people.

"It's not the low rates of vaccination, it's the fact that measles is such a contagious virus - it's the most contagious virus known to human-kind."

Anyone who suspected they had measles should avoid contact with other people, and call Healthline on 0800 611 116 or their general practice.

Those who were unsure about their vaccination status should talk to their doctor.