Products and retailers affected

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"Therefore we are advising anyone who may have any of these affected products at home not to consume them and to return them to the retailer."

One of the companies which has had to recall some of its products is Lyons Seafood.

It's chief executive, Ole Norgard, said he had no warning about the problem.

"It was a total surprise," he said.

"We understand that the FSA in Northern Ireland have a new test using new equipment to test for nitrofuran which is a synthtic compound.

"They tested 84 products out of which 15 were positive and out of them, five were Lyons products."

The company has already issued a recall on two of its brands.

A company spokesman said prawns from other parts of the world - like the North Atlantic - are not affected.

Risk assessment

The government watchdog is holding emergency meetings with retailers nationwide to discuss the problem.

The FSA has advised people who are concerned to contact the retailer where they bought the product or to log on to their website.

The prawns are contaminated with a substance called nitrofurans - which was banned for use in food production by European countries in the mid-1990s but still used in some areas of south east Asia.

The chemical was banned after it was found to have potentially carcinogenic - or cancer causing - effects.

Anyone eating the contaminated prawns can also experience dizziness, lethargy, headache, vomiting, chills, fever and abdominal pain.

A spokesperson for the FSA said: "We have carried out a survey in Northern Ireland and are looking at the results, while seeking expert advice in order to carry out a full risk assessment.

"We will be publishing a full result very shortly and issuing any necessary advice to consumers."

The shock discovery coincides with the European Union suspension on importing products of animal origin from China.

The embargo follows an EU inspection that unearthed lax controls in Chinese food production which can lead to residues and contaminants in imported products including rabbit meat, fish and shellfish.