Topping the list, Guotai Junan Securities said in a statement posted on the exchange website that its board approved an increase in equity investment to 20 percent of net assets (based on July 31 holdings), up from 15 percent (based on June 30 holdings) previously.
Guotai Junan has a market cap of about 150 billion yuan ($23.5 billion) according to Wind. For context, Goldman Sachs has a market cap of $79.1 billion.
Another major investment bank, CITIC Securities (market cap 177.3 billion yuan) added another 5.4 billion yuan, for a total of 21.1 billion yuan in investment, the company said in a document posted on the Shanghai exchange website.
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The Shanghai composite closed down 1.2 percent Tuesday, off nearly 40 percent from its June peak and down 2.1 percent for the year so far.
The Obama administration Tuesday urged China to explain policy changes and shift its economic focus toward consumer spending as the growth engine.
"Critical to China's success is moving forward with market-oriented reforms while at the same time carefully communicating policy intentions and actions to financial markets," a senior Treasury official told Reuters in a briefing ahead of a meeting of the Group of 20 major economies.
The Financial Times reported Monday that the Chinese government decided to shift away from fund injections and instead investigate and punish individuals for market "destabilizing." The government has already spent about $200 billion in the last two months to support the stock market, the FT reported.
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Late Monday, financial regulators issued a joint statement that encouraged firms to merge, offer cash dividends and buy back shares to support the market.
—Reuters contributed to this report.