The Hong Kong stock exchange is looking into the sudden plunge in Orient Overseas (International) Ltd (OOIL) shares in last-minute trading yesterday, which dragged the price down by nearly one-third to a 2 1/2-month low. The shipping company, which is controlled by former Hong Kong chief executive Tung Chee-wah's family, fell 31.95 per cent to HK$23, the largest drop since the stock began trading in 1992. The company was not aware of any reason for the share price movement and had no price-sensitive information that it planned to announce, OOIL spokesman Stanley Sham said yesterday. The shares were trading in a tight range at around HK$35 for much of the session before a bid of HK$26.50 was matched 45 seconds before the market close. Securities regulators are checking a mysterious selling order priced 24.28 per cent below the market price by a broker one minute before the market close. 'The stock exchange has noted the significant price movements in various transactions of OOIL at the last minute of the market close [yesterday],' a stock exchange spokesman said. Market watchers speculated that the sudden share price plunge could be the result of an initial trading error that other traders or programmed systems with unfulfilled sell orders were then compelled to follow. The exchange spokesman said the exchange has been in contact with the brokers who traded the shares in the last minute but so far no report of trading errors had been received. 'Suddenly, they find out they have some shares they haven't disposed of yet, so they will try to finish this order in the final minute, no matter what price it is,' said Ricky Tam Siu-hing, a director at Champlus Asset Management. Hong Kong Stockbrokers Association chairman Kenny Lee Yiu-sun said the Securities and Futures Commission and the exchange should undertake a comprehensive investigation to check on potential market manipulation in the stock. The exchange emphasised that both the SFC and the exchange had real-time market surveillance programmes to monitor trading activity and price movements of securities. Steve Cheng, associate director of Shenyin Wanguo Securities, discounted the suggestion of a trading error, or the so-called fat-finger mistake.