HONG Kong's stock brokers and floor traders, used to only 31/2 hours trading activity a day, could find themselves working longer. The stock exchange is pushing ahead with moves to extend trading hours. Stock exchange chief executive Paul Chow Man-yiu is proposing the doors of the bourse stay open for at least five hours a day in order to attract business from Europe. The exchange is open from 10 am to 12.30 pm and 2.30 to 3.30 pm, an arrangement seen by some as a hangover from colonial days. With increasing competition between international stock exchanges, the early closing in the afternoon allows for no overlap with London. That bourse is seen as one of the territory's biggest rivals as it accounts for 17 per cent of the trading of Hong Kong companies quoted on the exchanges in both cities. During the first five months of the year this was said to be worth $34 billion in lost commissions and fees. Mr Chow plans to bring Hong Kong up to date by keeping the market open until 5 pm, which will allow brokers in London to trade through Hong Kong when they arrive in their offices at breakfast time. ''We hope some transactions could be absorbed from London with an hour or more trading extended locally.'' He said there were several things to be considered, including shares settlement and custody. These had been held up in the past as reasons for not extending the trading hours. ''In addition, the winter and summer time difference between Hong Kong and London is to be considered as well,'' he said. But with the increasingly sophisticated computer technology this should not be a problem any more. Smaller brokerages are likely to be unhappy about the extension as it will increase the working day and their overheads. A similar move made recently by the Stock Exchange of Singapore sparked howls of protest from brokers. In its bid to attract international investors the Singapore exchange is open from 9 am to 5 pm and long lunch breaks are out.