Sell-by dates of discounted long life milk sold throughout the country will reach expiry within a few weeks, the Milk Producers Organisation (MPO) warned on Tuesday.

MPO managing director Etienne Terre'Blanche said an investigation into a sudden decrease in prices of ultra high temperature (UHT) milk showed many packets had a sell-by date expiring soon.

He said long life milk normally lasted up to nine months after purchase.

"Usually if people buy long life milk, they store it to use it much later."

A lot of the milk was imported, Terre'Blanche said, because of cheaper prices from overseas vendors. This in itself was not a problem since there was a dairy shortage in the country.

Some of the products were being sold for less than six rand a litre, while the current retail price was between seven and eight rand, according to the MPO.

Terre'Blanche said local dairy farmers were being victimised because supermarkets lowered the prices of their milk as well, which the farmers then had to subsidise.

He said the milk was not harmful after the date had expired, but it would result in a loss of nutrition value, it would taste bad and one would feel nauseous after drinking the milk.