The mainland's overseas investment could rise to US$4.46 trillion, or 54 per cent of gross domestic product, if the capital account is fully liberalised, according to a Hong Kong Monetary Authority study. The growing investment should benefit the Hong Kong financial services industry, it said. Mainlanders are not allowed to invest freely outside the country, but the authorities have gradually relaxed the capital account with initiatives such as the qualified domestic institutional investors scheme early this year. 'With national savings amounting to 50 per cent of GDP and limited investment opportunities in the domestic market, this represents a large amount of funds to be invested abroad should restrictions on outward capital flows be relaxed,' the de facto central bank said in its quarterly bulletin. If China's capital account were as open as that of a typical industrialised country last year, its overseas portfolio investment would reach US$340 billion, or 15 per cent of GDP, and Hong Kong would capture close to 10 per cent, or US$32 billion, of the investment, the study said. The actual size of China's overseas investment last year accounted for 5 per cent of GDP. The HKMA said in the report that retail banks continued to make a steady profit as net interest margins widened to 1.79 per cent in the third quarter from 1.74 per cent in second and 1.66 per cent a year ago.