Authorities yesterday revealed figures showing more than $33 million worth of gems and jewellery had been reported stolen this year from Asia's two biggest jewellery fairs, both held in the Convention and Exhibition Centre.

Nearly $14 million in diamonds and jewels have been stolen over the past week from exhibitors during the five-day Hong Kong Jewellery and Watch fair, which ends today.

Security officials are on their highest state-of-alert for the final day of business - traditionally the most vulnerable to sophisticated overseas gangs - when many of the 1,200 exhibitors start moving packages of diamonds, jewels, gold, silver and pearls to other venues.

Police intelligence reports indicate that highly organised gangs known to be targeting the Hong Kong event include South American and Colombian gangs, Indian-Pakistani syndicates and mainland China triads.

Security measures under discussion include allowing private security firms to carry weapons inside the venue, enhanced security briefings and awareness among industry operators and a crackdown on insurance-related scams to thwart dodgy claims by unscrupulous jewel traders.

Detective Chief Inspector Bob White, of the Crime Prevention Bureau, said it was not known why the city suffered such a high percentage of thefts in relation to similar events. But some investigators suspected some of the reported thefts might be 'inside jobs'.

'There is an element of concern about the old-fashioned insurance scam,' Chief Inspector White said.

This may be a jeweller who needs the money or is looking to get rid of some old stock that might be old-fashioned or out of style.

'But proving these scams is an entirely different thing,' he said.

Chief Inspector White said the Colombian and South American gangs were considered by law enforcement agencies as being among the world's most prolific jewel thieves.

Two Venezuelans, a man, 25 and woman, 24, were arrested on Friday at a Jordan guesthouse in connection with the theft of 200 diamonds worth $7.8 million from a booth at the exhibition. But there is no trace of the missing diamonds.

'There has been much discussion about the installation of facial recognition systems, hooked up to CCTV and a computer database, which sends out a signal when it detects one of the suspects,' Chief Inspector White said.

'But there are practical problems such as having an available database of suspects, as well as dealing with the sheer volume of people. And of course they will mostly be operating in disguise and in teams and will be very aware of any close surveillance.'

He said the most common methods employed by the gangs were the 'sleight of hand' or the 'extremely attractive lady customer' who distracts staff while other gang members snatch the jewels.

Internationally renowned jeweller and Israeli diamond manufacturer Ilan Samuel yesterday said Lloyd's of London insurance rates had nearly trebled for most exhibitors visiting the Hong Kong event because of the rising spate of thefts.

He said he became aware of the methods of international thieves after being robbed of a US$250,000 bag of diamonds at a jewel fair in Europe several years ago.

'They do their homework and operate like a family,' Mr Sameul said.

'If someone gets caught, they organise the lawyers.

'They do not talk, they do not crack. And they never kill, never hurt anybody, they just steal.'