(Bloomberg) -- A third Hong Kong stock in less than a week lost most of its value in a sudden one-day plunge, underscoring concern that the $5.2 trillion market has become a breeding ground for wild volatility.

China First Capital Group, an investment company that focuses on financial and education services, plunged as much as 78% on Wednesday before trading was suspended. Virscend Education Co., which is partly owned by First Capital, also lost as much as 78% before paring its decline to 32%.

Virscend suspects its shares were sold by First Capital because of a margin call, but has not verified anything, said Chen Keyu, Virscend’s director of investor relations. First Capital said it couldn’t immediately comment.

While Hong Kong is no stranger to sudden stock slumps, the fresh wave of declines is once again putting the spotlight on corporate governance at the city’s listed companies.

Last week, ArtGo Holdings Ltd. slumped 98% after MSCI Inc. scrapped plans to add the stock to its benchmark indexes, citing concerns about its investability. That same day, a Chinese furniture maker fell as much as 91% after a short-seller questioned the company’s accounting. First Capital owned a 1.6% stake in ArtGo as of July, according to an exchange filing.

Read more: Why Hong Kong-Listed Stocks Can Go On Such Wild Rides

Hong Kong’s Securities and Futures Commission and stock-exchange operator have made cleaning up the city’s equity market a priority in recent years, saying extreme share-price swings and allegations of manipulation -- particularly among small-cap stocks -- have damaged the Hong Kong’s reputation. The collapse in 2017 of a shadowy group of companies, dubbed the “Enigma Network” by local activist investor David Webb, is now part of the biggest investigation of market malfeasance in the city’s history.

China First Capital reported a net annual loss in three of the past four years, according to data compiled by Bloomberg. The company has pledged assets worth about 758 million yuan ($108 million) for unspecified funding purposes, according to its mid-year earnings report. It held a stake of about 12.4% in Virscend, according to an exchange filing in July.

China First Capital is a constituent of China-focused indexes compiled by MSCI and FTSE Russell. As a member of the Hang Seng Composite index, it’s also available to mainland investors through stock links with Hong Kong.

--With assistance from Elena Popina.

To contact Bloomberg News staff for this story: April Ma in Beijing at ama112@bloomberg.net;Jeanny Yu in Hong Kong at jyu107@bloomberg.net

To contact the editors responsible for this story: Sofia Horta e Costa at shortaecosta@bloomberg.net, Michael Patterson

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