CHINA Overseas Land and Investment plans to seize the opportunity presented by the slump in the mainland property market to expand its land bank in big Chinese cities. The mainland-controlled property developer currently owns 5.77 million square feet of land, most of it in Shanghai, Guangzhou and Shenzhen. Vice-chairman and general manager Sun Wenjie said the company would find new sites in major cities. ''The introduction of macro-economic control measures may mean some developers are unable to go ahead with projects,'' said Mr Sun. ''We will take the opportunity to buy prime sites at lower prices and we are optimistic that long-term prospects are good.'' China Overseas is a subsidiary of building group China State Construction Engineering Corp. Mr Sun said he believed measures to cool the economy introduced in the middle of this year would be relaxed next year. ''At that time, demand in the mainland property market will pick up,'' he said. Mr Sun said China Overseas had succeeded in the mainland by buying at the right moment. It was active in the China property market in 1988, well ahead of most Hong Kong developers. ''But when others were still rushing into China some time ago, we were slowing down our investment there because we felt the mainland property market was a bit overheated,'' said Mr Sun. ''Now that some of the developments are not going smoothly, we will take this opportunity to replenish our land bank. This is our success strategy.'' Nevertheless, he said, China Overseas would continue to be cautious about the mainland. ''Although rewards on the mainland may be attractive, the choice of site is important. If you go to the wrong city, sales will be quite difficult,'' he said. He said Beijing's economic controls would not affect China Overseas' sales because most of its projects would not be sold until 1994 and 1995. Mr Sun said the Hong Kong property market would continue to grow steadily in the next few years. While the market's overall performance this year would be better than last, the property and construction sub-sectors were not progressing as well as expected. ''This is mainly because some of the major banks introduced tighter mortgage lending restrictions on the local property market,'' he said. Mr Sun said China Overseas would try to diversify its business in the next three to five years. Seventy per cent of its revenue would come from property, 15 per cent from construction and trade, and the remaining 15 per cent from industrial investments in China. ''This will make for a better mix of high-yield and stable businesses,'' he said. He said China Overseas was talking to mainland enterprises about possible acquisitions in the cement, timber and brick-making industries.