Mainland stock exchanges have amended rules spelling out when they may temporarily suspend trading in companies with volatile price swings and turnover. The Shanghai and Shenzhen exchanges - in notices to leading financial newspapers yesterday - said the amendments made clear for the first time the circumstances under which they could exercise their powers to suspend companies: when its share price hits the 10 per cent limit up or down in three consecutive days; when its daily share price fluctuates 15 per cent for three consecutive sessions; when its daily turnover is 10 times the daily average of the previous month for five consecutive sessions; when the exchange or securities watchdog deems its trading abnormal; when the company is required to disclose material trading information in five straight days. Exhange officials said the latest moves would tighten supervision of trading, with an eye on risk control. The amendments came as the exchanges were apparently concerned with the dramatic rise in the share prices of companies with asset injection or restructuring potential. Before its month-long suspension from May 14, Shenzhen Wellzone Chemical Fibre saw its price spiral 115 per cent from April on rumours of restructuring of listed textile companies. Earlier this week, Shanghai Fourth Pharmceuticals was suspended, also for a month, amid talk of plans to expand equity and restructure. The company's share price has risen 114 per cent since January. Analysts said the amendments represented another step in standardising market behaviour, although they might not necessarily help to explain abnormal swings in share price or turnover. Shenyin & Wanguo analyst Zhou Liang said: 'The supplementary amendments mark another step in standardising market behaviour, but not all steps will be effective in checking volatility.' Shanghai Finance Securities analyst Zheng Weigang said: 'In recent months, prices of certain shares have risen dramatically, with some rising more than 100 per cent. 'The latest rules may be authoritative, but may not be effective as dramatic share rises are due more to insider trading than anything else.'