China's credit card transactions totaled 3.5 trillion yuan (512.45 billion U.S. dollars) in 2009, up 69.9 percent from a year earlier, said a report from the China Banking Association (CBA) Wednesday.

By the end of 2009, China had issued 186 million credit cards, up 30.37 percent from a year earlier, said the report.

Credit card transactions accounted for 27.9 percent of the total social retail sales in 2009, up from 11.2 percent in 2007, said the report.

The association warned of potential risks of the increasing overdue credit card debt, as the country's lenders continued to expand their credit card business.

China reported 5.27 billion yuan (765.30 million U.S. dollars) of credit card bad loans in 2009, up 78.68 percent from a year earlier, said the report.

The industry was taking measures to guard against risks as relative rules, laws and procedures in credit card markets were yet to improve, said Yang Ke, an official with the association and President of the Credit Card Center of China Minsheng Banking Corp. Ltd..