Central Huijin Investment Co, which holds Beijing's investments in state-owned financial firms, spent about 363 million yuan ($59.2 million) buying bank shares on June 13, Reuters calculations based on stock exchange filings showed.

This is the third time Huijin has been known to be buying shares in the secondary market since June 13, when China's stock market <.CSI300> skidded to six-month lows after data showed the world's second-biggest economy was cooling faster than expected.

Despite China's promise to allow free markets to play a bigger role in its economy, Beijing regularly intervenes in the equity market during sell-offs by ordering Huijin or other state pension funds and insurers to invest millions or billions of yuan in shares.

In its latest intervention, Huijin, a unit of China's $500 billion sovereign wealth fund , scooped up shares in Industrial and Commercial Bank of China (ICBC) <1398.HK>, Bank of China (BoC) <1288.HK>, China Construction Bank (CCB) <0939.HK> and Agricultural Bank of China (ABC) <1288.HK>.

All four banks said in statements that they expect Huijin to further raise its stakes in them over the next six months.

Just last week, Everbright Bank (>> China Everbright Bank Co., Ltd) and New China Life Insurance (>> New China Life Insurance Co Ltd) (>> TCC International Holdings Limited) said Huijin had raised its stakes in them with more than 100 million yuan in investments.

Chinese media has also reported that Huijin has bought 5.2 billion yuan worth of shares in three exchange-traded funds that invest mostly in blue-chip stocks.

Such interventions usually give a fillip to share prices although the market has in the past surrendered those gains over time.

For instance, Huijin ploughed $470 million into Chinese bank stocks in October after investor concerns about rising bad debt pummelled the shares to their lowest in nearly four years. The purchase preceded a rally in Chinese bank stocks to their highest in nearly two years, but prices have since fallen back by about at least a fifth.

Following Huijin's latest purchases, China has raised its stake in each of the four banks by 0.01 percent each and now owns 35.46 percent of ICBC, 67.74 percent of BoC, 57.23 percent of CCB, and 40.24 percent of ABC, stock exchange filings showed.

($1 = 6.1308 Chinese yuan)

(Reporting by Aileen Wang and Koh Gui Qing; Editing by Jason Subler and Susan Fenton)