Seven people are confirmed to have contracted campylobacter after drinking raw milk purchased from a farm on the outskirts of Timaru.
In warning people of the risks of drinking raw milk, medical officer of health Daniel Williams described the confirmed cases as the "tip of the iceberg".
The supplier, Timaru Village Milk, announced the outbreak on its Facebook page on Wednesday.
"We have been notified of a campylobacter presence in the milk.
We will stop selling milk until the milk test results show that the milk is clear of this problem for two consecutive days."
The statement by Mark Houston said it could take a week to get assurance the milk was safe.
Village Milk also has franchises in Oxford, Greymouth, Takaka, and Moutere.
RAW MILK CAN BE 'DANGEROUS'
Williams said drinking raw milk was "risky". "It can contain disease-causing bacteria and other organisms which can lead to gastroenteritis and other illnesses, some of which can be life-threatening,'' Williams said.
The young, elderly, pregnant women and people with weakened immune systems were at greatest risk.
''Most milk sold in New Zealand is pasteurised, which means it has been heated to kill harmful bugs.''
Williams said even drinking raw milk from suppliers with the highest hygiene and safety standards could be dangerous as any raw cow milk could contain bugs.
If a person felt unwell within a week of consuming raw milk, he advised them to see a doctor.
The Ministry for Primary Industries (MPI) has conducted an investigation of the milk producer.
New Zealand legislation allows producers to sell up to five litres of raw milk daily at the farm gate to people buying it for themselves or their family.
Consumers can reduce the risk of getting sick from drinking raw milk by heating raw milk up to 70 degree Celcius for one minute or to 63C for 30 minutes.Â