Mainland-backed China and South Sea Bank has raised its residential mortgage rate by 0.5 per cent to limit its exposure to the property sector. The announcement followed a stern warning by the Hong Kong Monetary Authority on Monday urging banks to slow home-loan growth or risk a range of penalties. The bank's new mortgage rates will range from 0.75 to 1 per cent over the prime 8.75 per cent rate. Assistant general manager Daniel Ng Sai-wing said the move was not directly related to the authority's warnings but part of the bank's internal controls to limit its risk exposure. He said the bank wanted to control any increase in its loan-to-deposit ratio, which stands at more than 50 per cent. Another mainland-backed bank, Yien Yeh Commercial Bank, raised its mortgage rate a month ago, saying it had achieved its quota for the year and did not want to accept more home loans. Wing Hang Bank's head of product development Stephen Wong said the bank would stick to its plan of reducing its property exposure by securitising part of its mortgage portfolio, which would come into effect this year.