Dr Wong was speaking at a Baptist University ceremony yesterday where four Hong Kong producers received certificates allowing them to put the centre's seals on their goods. The four organisations - Peninsula Innovation, Hong Kong Organic Country, Kam Kee Farm and the Vegetable Marketing Organisation - were the first to be accredited by the centre.

In a survey of 600 samples of fresh vegetables, dried fruits and nuts, the centre found that only 29 per cent were properly certified. Out of the 71 per cent not certified, 34 per cent claimed to be organic.

'Some producers label their products organic but do not actually have any certification, which means they may or may not be organic,' Dr Wong said.

Others have ambiguous labelling. A mainland producer, Green Food, claims its food is 'green' on the packaging and the products are often put in the organic section in supermarkets. However, the small print shows green actually means they do not use excessive levels of pesticides or fertilisers.

Other producers claim they do not contain genetically modified organisms, which people may misunderstand to mean no pesticides or fertilisers are used.

There are no laws in Hong Kong to stop farmers from labelling themselves as organic or green.

Dr Wong said: 'To protect consumers, the government needs to consider setting up a set of local organic standards and a certification system, like the National Organic Programme in the US where everybody follows the same standard.'

Farmers who are trying to convert from conventional farming - using pesticides and fertilisers - to organic farming now show a VMO (Vegetable Market Organisation) logo, which means they are following the Agriculture, Fisheries and Conservation Department's protocol of organic farming.

Although they make up less than 1 per cent of the market share in Hong Kong, the trend for organic foods is on the rise.

'After Sars and bird flu, people became more concerned with their health,' Dr Wong said.