DISCLOSURE rules for both Hong Kong and mainland companies are to be tightened by the stock exchange, and banks sponsoring mainland share issues are warned that they must live up to their obligations to their clients. Among the information which would have to be disclosed would be interim profit figures, said the exchange, which is also planning to introduce key guidelines for the valuation of mainland companies' plant and machinery. Head of listing Herbert Hui Ho-ming yesterday said: ''I'm looking, as a general rule, to see whether companies should make a first detailed announcement about their interims and I'll make a recommendation to the stock exchange committee as soon as possible.'' He added that Chinese regulatory authorities would continue to control the listing of mainland companies in Hong Kong despite hopes among merchant and investment banks that the planned second batch would be more diverse than the original ''mainland nine''. The insistence of the publication of all interim figures follows disquiet over the decision by Tsingtao Brewery not to publish interim figures. That it was under no obligation to do so deeply concerned international investors although existing rules do exempt some companies. Mr Hui also said that the stock exchange ''is addressing this whole area of valuation in the context of the mainland listings and will be talking to industry professionals''. The first nine companies chosen for listing in Hong Kong are mainly in heavy industry. So far, six have been floated. Because Hong Kong does not have any heavy industry, its listing rules do not provide for guidelines for valuing machinery and equipment. As a result, Hong Kong companies doing valuations for mainland companies listing in the territory have had to turn to American or European standards. American Appraisal Hongkong vice-president Keith Yan said that because the existing listing rules were not designed to cover companies in large-scale industries such as the nine Chinese corporations being listed here, valuations for them had been daunting. ''With these Chinese companies, the machinery and equipment may actually be more valuable than the land and the buildings,'' he said at a seminar organised by the Asian Law Journal. That was the case of Shanghai Petrochemical, the second mainland company listed here, which had machinery and equipment worth about eight billion yuan (about HK$10.72 billion at the official rate), more than twice the value of its real estate. Because it was uncommon for a Hong Kong valuation to have the expertise to value machinery and equipment, experts from overseas, especially the US, had to be brought in to help Hong Kong staff to do the job. Mr Hui also lashed out at some merchant banks which failed to live up to their obligations as sponsors of the mainland companies, but he did not name the culprits. ''It's written in the listing rules for PRC companies that the sponsor must stay with the companies for three years,'' Mr Hui said. ''But on a day-to-day basis, there are times when we find it difficult to communicate with the merchant banks which are supposed to be sponsors but which, basically, after listing, deny any further responsibilities. ''This is irresponsible. There are five sponsors and I don't want to be specific.'' Mr Hui said the sponsors should not walk away from the Chinese companies which needed help to see them through the transition from being state-owned to publicly-listed. ''The merchant banks bring these companies to the market and they should stick with them to make sure that they understand what the requirements are,'' he said.