(Bloomberg) -- There’s nothing like margin calls to make a bad stock-market selloff even worse.

It’s a risk at the top of investors’ minds in China after the nation’s $3 trillion equity rout deepened on Thursday, driving the Shanghai Composite Index to a nearly four-year low.

With more than $600 billion of Chinese shares pledged as collateral for loans, or about 11 percent of the country’s market capitalization, the worry is that falling stock prices will trigger a downward spiral of forced selling. The country’s top financial regulators sought to reassure investors on Friday that they’re able to keep risks under control.

But some stocks are more vulnerable than others. At least 144 Chinese companies have more than half their shares pledged, often the result of founders using their stakes to raise cash, according to clearing house figures compiled by Bloomberg. Of those, 60 have seen the value of their shares tumble by more than 50 percent this year.

The table below lists some of the biggest companies that fit both those criteria, with a couple of important caveats: Some companies may have pledged restricted shares, which would mean they’re ineligible for immediate liquidation even after steep losses. Levels that trigger margin calls or forced selling may also vary, depending on the timing and terms of the loan.

To contact Bloomberg News staff for this story: Sofia Horta e Costa in Hong Kong at shortaecosta@bloomberg.net;Amanda Wang in Shanghai at twang234@bloomberg.net

To contact the editors responsible for this story: Richard Frost at rfrost4@bloomberg.net, Michael Patterson

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