Foreign investors piled into China’s policy bank notes at a record pace last month as efforts to open up Chinese markets into the global financial system help buoy inflows.

They bought a net 50.7 billion yuan ($7.3 billion) of the notes in May, a month that saw foreign holdings of Chinese bonds rise the most this year. That’s according to ChinaBond data going back to July 2014, which covers about 83% of the holdings. The Shanghai Clearing House typically publishes the remaining data by the 10th day of any given month.

Foreign inflows have been spurred by efforts to open up the debt market, such as the recent index inclusion, said Raymond Yeung, chief economist for Greater China at ANZ Banking Group. The Bloomberg Barclays Global Aggregate Index is adding securities issued by the government and its policy banks over a 20-month period that began April 1. Policy banks have been issuing bonds to fund loans offered to local governments for infrastructure spending.

China’s waiver of corporate tax on interest income made by overseas institutional investors in the bond market is also helping to stoke appetite, said Gordon Tsui, head of fixed income at Taikang Asset Management Co. in Hong Kong, adding that policy bank bonds outshine government bonds in terms of liquidity and returns.

The notes were the most popular in terms of monthly trading volume on Bond Connect, followed by negotiable certificates of deposit and Chinese government bonds. The U.S. overtook Hong Kong with the highest market share for accounts opened for Bond Connect, Hong Kong Exchanges & Clearing said last month.