Chinese banks bought more foreign currency than they sold in April, the ninth consecutive month of net foreign exchange purchases, China's forex regulator said on Tuesday.

Chinese lenders bought $150.6 billion worth of foreign currency in April and sold $140.9 billion, resulting in a net buy of $9.7 billion, the State Administration of Foreign Exchange (SAFE) said in a statement.

The run of net forex purchases began in August 2013, but the surplus has been narrowing, [company registration in Hong Kong, Hong Kong company incorporation]down from $40.2 billion in March, $45.7 billion in February and $73.3 billion in January.

In the first four months of 2014, Chinese banks bought $667.3 billion in foreign currency and sold $498.4 billion, bringing the net purchase volume to $168.9 billion, according to the SAFE statement.

Forex transactions are a major cause of fluctuations in China's forex reserves. Surpluses may suggest pressure from trans-border capital inflow.