WITH a 30 per cent to 40 per cent projected growth for its card activity in China in 1994, American Express (AMEX) is poised to maintain its biggest slice of the thriving market. It currently has a 50 per cent share of the mainland market, while Visa International and MasterCard combined possess about 40 per cent. Despite its leading position in the market, AMEX is still restricted by Beijing's policy in the sector. ''China is taking careful steps in building up its financial infrastructure, but before the time comes for a freely convertible yuan and foreign card companies are allowed to handle forex transactions, AMEX finds it hard to go into the yuan card business,'' said American Express Company vice-chairman Jonathan S Linen. Although China remains a cash society, it is expected that the acceptance of cards as a payment system will ultimately lead to an American-style consumer credit card market. Eugene Xi, American Express International Beijing representative office chief, believed that there would be better prospects as soon as China re-entered GATT and the yuan became freely convertible. For AMEX, 88 per cent of its payment volume is hotel-related, and an average payment per person is about US$200 (HK$1,544), double those of other cardholders. Mr Xi said the major cities, Beijing, Shanghai and Guangzhou accounted for 33 per cent, 28 per cent and 35 per cent of income respectively. AMEX struck a deal with China National Tourism Administration (CNTA) last week, making AMEX Card the official card of tourism for China up to 1997. CNTA marketing and promotion director Yang Linyin said the agreement was significant.