The chairman of the Gemmological Association of Hong Kong, Louis Lo Yick-sun, said that previously diamonds that weighed more than one carat were taken overseas for testing, and stones under one carat were not tested.

Now they could all be certified in Hong Kong more quickly and at a lower cost.

The certification covers the clarity grading, colour, fluorescence, authenticity and weight of the stone.

Consumer Council executive director Connie Lau Yin-hing welcomed the standard, saying: 'We believe it can certainly give assurance to consumers.'

Jewellery Chain Luk Fook Holdings (International) said its subsidiary company China Gem Laboratory would consider participating in the accreditation scheme.

Wholesaler Simon Chan, of Mei Fung Jewellery, said the new standard would benefit retailers and consumers by giving them more confidence about what they were buying.

Another wholesaler, Stanley Chiu from Artistic Jewellery, said diamonds that weighed 20 points or less were too small to be certificated.

Jewellery designer Karen Lee said adopting the testing scheme was a positive step.

But she was concerned that, if not well promoted internationally, the new standard might cause confusion among buyers who did not understand it.

The 25th Hong Kong International Jewellery Show began yesterday by setting a fair record, with more than 2,300 exhibitors from 45 countries and regions taking part.

Cambodia, Egypt, Lebanon, Kuwait and Mexico are participating for the first time.

Last year's show attracted 31,000 buyers, and the number of buyers registered online has grown this year.

It continues until Saturday at the Convention and Exhibition Centre in Wan Chai.