THE Netherlands' exports to Hongkong have doubled in less than two years according to the trade Consul, Mr Klaas Ruijg. Overall trade growth has averaged 20 per cent per year for more than a decade, but leapt to more than 60 per cent last year on the back of a four-year nickel boom. The Netherlands imports the nickel ore, treats it and exports the clean non-ferrous metal to Hongkong. The value of nickel exports in 1992 was just under HK$2 billion - representing a rise of more than 400 per cent on the previous year. ''Electrical equipment manufacturers apparently buy nickel in bulk at three or four yearly intervals. It gives our trade pattern rather an uneven look, but we don't mind,'' Mr Ruijg said. The principal Dutch exports to Hongkong are dyeing, tanning and colouring materials for the garment industry, a variety of electrical machinery and appliances, dairy products and eggs, clocks, optical goods and photographic equipment, organic chemicals, plastics and book-binding machinery. Of these, the photographic and book-binding categories also recorded substantial rises in 1992, by 301 per cent and 134 per cent respectively. About 16 per cent of Dutch exports to Hongkong are re-exported into China, mainly to Guangdong. As Consul, Mr Ruijg's twin goals are the promotion of Dutch exports and the stimulation of inward investment to The Netherlands. There are 180 Dutch companies represented in the territory, with 28 using it as the site for their regional headquarters. About 1,700 Dutch nationals live in Hongkong, although this number is likely to grow substantially as the Chek Lap Kok airport project develops. ''At present, we have five major dredging companies from The Netherlands working on the West Kowloon and Chek Lap Kok reclamations,'' Mr Ruijg said. ''Senior Dutch managers are increasingly bringing their families to Hongkong, even though the reclamation contracts must be completed by 1995. ''However, many are thinking longer-term, because we are confident that Dutch expertise will be strongly involved in bidding for, and winning, the airport terminal contracts. ''Remember, Schiphol won the award from the annual Cargo News survey as the best airport outside Asia, for the fourth time last year, and Rotterdam won the equivalent award for sea ports,'' he added. Hongkong retains the title as the world's busiest container port, but if grain, oil and ore carriers are included, the mantle of 'world's biggest port' passes to Rotterdam. Hongkong's domestic exports to The Netherlands fell by seven per cent in 1992 as against the previous year, but still amounted to almost $5 billion. But re-exports more than compensated for this, climbing over 35 per cent to reach $9.7 billion, for a total of $14.6 billion. Principal exports were clothing and accessories, closely followed by office machinery and automatic data processing machines. The Dutch are serious about their commitment to Hongkong and the stimulation of business. The Netherlands Consulate General has direct lines to the Hongkong General Chamber of Commerce and to the Trade Development Council to facilitate the provision of immediate information or action. In The Netherlands there is not only the China Hongkong Trade Centre, based near Rotterdam, but also a branch affiliate of the Trade Development Council. Additionally, Hongkong Bank has a presence in The Netherlands through its British-based subsidiary Midland Bank. Mr Ruijg said that 40 per cent of Japanese companies in Europe had their headquarters in Holland, largely because of the advantageous tax structures.