HONGKONG'S Convention and Exhibition Centre will be virtually doubled in size before 1997, following approval of a $2.4 billion extension on land gained from the Central and Wan Chai reclamation project. Mr Macleod announced that he was earmarking the cash for construction of an extension in front of the Harbour Road centre. Another $3.1 billion would be allocated to pay for the reclamation and service work on the site, which stretches 300 metres into what is now Victoria Harbour. Mr Macleod said the centre, which is run by the Trade Development Council (TDC), ''has proved to be a huge success, bringing substantial economic benefits to Hongkong''. ''But the centre is fast reaching the limits of its capacity. The council has suggested the construction of an extension in front of the existing centre. ''I expect the extension to bring about quantifiable economic benefits amounting to some $9 billion to $10 billion a year, in addition to those unquantifiable benefits such as absorption of new knowledge and ideas brought to Hongkong through the holding of conventions and exhibitions.'' It is believed that Mr Macleod's estimate of benefits includes charges levied by the centre on conference organisers, together with revenue to hotels, airlines, travel organisations and retailers from delegates visiting the territory. TDC chairman Dr Victor Fung Kwok-king said the extension would help Hongkong remain the trade fair and conference capital of Asia. ''There is no time to lose because the existing centre is already operating close to capacity and demand is continuing to grow. We are ready to proceed to detailed planning immediately.'' Dr Fung added that the work was vital because regional competitors were already building or upgrading their own facilities. Currently, the centre, which cost $2.25 billion when it was opened in 1988, has 18,000 square metres of exhibition space and conference hall facilities that can accommodate 3,000 people. It will host more than 1,000 exhibitions, conferences and corporate events this year. The extension aims to provide an extra 30,000 to 35,000 square metres of space for another 5,500 customers. The present facility lags behind Seoul, Taipei, Singapore and Jakarta in the amount of exhibition space available. Seoul tops the table with 31,000 square metres of space in its conference centre, while the other cities have between 22,000 and 27,000 square metres in their major venues. A TDC source said construction was expected to take about 31/2 years and the new building - which would probably be linked by walkways to the current centre - would be finished by 1997. Mr Macleod said he had been urged by the TDC to give more money to industry support activities such as research and development to help manufacturers move into hi-tech production. He also hinted that the days of the TDC being financially propped up by the Government could end. ''There is also a need to rationalise the TDC's funding arrangements in recognition of its success in generating income. This may well enable us to increase the funds for supporting industry,'' he said. The chairman of the Hongkong Exhibition and Convention Organisers and Suppliers' Association, Mr Derek Dickens, said the territory would be able to bid for major expositions well into the next century once the extension was completed.