INVESTORS should brace for more new financial products after next week's launch of the Hang Seng China Enterprises Index (HSCEI) as futures and options based on the new H-share index and an index for medium-size companies in Hong Kong come on stream. The HSCEI, which will appear on the TeleText system of the stock exchange and the Reuters screen on Monday, will provide a composite picture of the movements of H-share prices for the investment community. It comprises all 10 H shares. With a calculation formula identical to the 25-year-old Hang Seng Index, constituent stocks are weighted by their market value. The base value is set at 1,000 on July 8, the date when the 10th H-share company, Luoyang Glass, was listed. At yesterday's close, the index rose to 1,297. The total market value for the 10 stocks stands at $15 billion, with two companies accounting for half of the value. Maanshan Iron and Steel takes up 30.15 per cent of the weighting with its $4.76 billion market value, and Shanghai Petrochemical is second with $3.71 billion, or 23.49 per cent of the pie. The smallest share comes from Kunming Machine Tool, with only a 1.32 per cent weighting in the index. The index was born out of a need for a more focused indicator of the overall performance of Hong Kong-listed China enterprises which have drawn considerable interest from the global financial community. The allure of H shares attracted total turnover in June of $1.44 billion. Dongfang Electrical Machinery topped the list with $727 million in turnover. More stocks will be incorporated into the index and the market expects to have more than 20 H-share companies listed by the end of 1995. ''We are sure the new market barometer will be widely used in the future to monitor developments in those sectors of the Chinese economy represented by the stocks included in the new index,'' said Alexander Au, managing director and chief executive of Hang Seng Bank. Apart from reflecting the trading activities of the H shares, the new index will form a basis for more derivative products. The chief executive of the Hong Kong Futures Exchange, Ivers Riley, said the exchange would launch futures and option instruments on the new index. ''The exact timing will have to depend on market circumstances but the futures will come first,'' he said. Both the new index and the Hang Seng Index are compiled and managed by Hang Seng Index (HSI) Services, a wholly owned subsidiary of Hang Seng Bank. Having invested about $2 million in the HSCEI, the company is already conducting preliminary discussions on launching an index of medium-sized companies. ''That will include the non-Hang Seng Index stocks, probably the second-liners and third-liners. It will be determined by their market capitalisations,'' said Roger Luk, chairman of HSI Services. Further details have yet to be fleshed out, he said. While the HSCEI had only 10 constituent stocks, the chances of limiting the number, as in the case of the Hang Seng Index's 33 constituent stocks, were remote, Mr Luk said. Unlike other H-share index providers in the market, Mr Luk said HSI Services was an independent index compiler which did not engage in stock trading activities. The new index will be disseminated through the channels that exist for the Hang Seng Index.