New Zealand's South Island is grappling with a measles outbreak, with authorities warning the number of confirmed cases is expected to "rise further over the coming days and weeks".

Key points: More than 20 confirmed measles cases have been reported in the Canterbury district since last month

More than 20 confirmed measles cases have been reported in the Canterbury district since last month Around 18,000 MMR vaccines are expected to be brought into the region by Wednesday

Around 18,000 MMR vaccines are expected to be brought into the region by Wednesday The latest outbreak came from people who were not fully immunised, New Zealand's Health Ministry said

Thousands of vaccines are being delivered to health centres in the Canterbury district, which includes Christchurch, as the potentially life-threatening disease widened to more than 20 confirmed cases.

Clinics in the central-eastern region ran out of vaccines after the outbreak started in late February, with an additional 18,000 MMR vaccines expected to be brought in by Wednesday.

"It can now be assumed that measles is circulating widely in our community," the Canterbury District Health Board said in a statement.

The latest outbreak came from people who were thought to be not fully immunised.

People are considered immune if they have received two doses of the MMR vaccine, have had a measles illness previously, or were born before 1969.

One in 10 people who get measles will need treatment in hospital, and up to 30 per cent will develop complications — usually children under five and adults over the age of 20.

"Unimmunised people who come within 2 metres of an infectious person, however briefly, have a 90 per cent chance of contracting measles," the board said.

Measles cases are rising globally, including in wealthy nations such as the United States and Germany, where some parents shun the vaccines mostly for philosophical or religious reasons, or concerns — debunked by medical science — that the vaccine could cause autism.

New Zealand's Ministry of Health said in a statement that since 2012, all cases of measles in the country came from overseas.

"Since the beginning of this year, New Zealand has seen an increase in measles cases," it said.

"All of these cases followed a measles case imported from overseas. There are currently three ongoing outbreaks, two in the Waikato and a new one in Christchurch."

ABC/Reuters