O'Connor, for its part, is among a small group of hedge funds that have already participated in the quota program, named the qualified foreign institutional investors program. They buy and sell shares denominated in both renminbi and Hong Kong dollars.
The wide-open connection will allow hedge funds like O'Connor to expand their business between the two exchanges and trade directly.
Still, challenges remain, and some significant questions have not been answered.
The program is part of a broader reform package announced by President Xi Jinping last year. Critics point to other reform initiatives, like the building of new and planned free trade zones, that have been slow to take off.
Last September, regulators in Shanghai agreed to let a small group of United States and British hedge funds raise $50 million each from Chinese investors as part of a pilot program. One of these firms has complained that progress has been slow and weighed down by bureaucratic hurdles.
Linking the Hong Kong and Shanghai exchanges is not a new idea. In 2007, Hong Kong officials announced a similar plan to allow Chinese investors to gain access Hong Kong's stock market. That plan never took off.
And while foreign and Chinese investors will have the chance to invest in hundreds of companies that were previously off limits, they will still be limited by quotas. The combined two-way trading volume will be capped at 23.5 billion renminbi ($3.8 billion), about 20 percent of the combined average daily trading volume on both markets. Individual mainland Chinese investors will need at least 500,000 renminbi in their brokerage account to buy Hong Kong shares, a threshold that excludes most retail investors.
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Foreign buyers of Shanghai stocks will not be able to buy shares and sell them on the same day. It is still unclear whether they will be allowed to buy shares using margin financing or to engage in short-selling. And, in another hurdle, all trades will be settled in renminbi, introducing additional risk for foreign investors.
There are also unresolved issues over taxes. Foreign investors in mainland China's stock markets are technically liable for paying capital gains taxes, but China has historically not taxed such investments under the existing quota scheme. It remains an open question whether that practice will change.
Given these and other uncertainties, companies like MSCI — which compiles indexes that are tracked by funds with trillions of dollars invested in stocks around the world — have so far declined to include mainland Chinese shares in their indexes.
That could change as soon as next year, when MSCI is next scheduled to review Chinese shares.
"Were China's domestic A-shares to be included in the MSCI benchmarks, it would be a game-changer, attracting billions of dollars of capital," analysts at HSBC in Hong Kong wrote this month in a research report.
Regardless, some investors are pushing ahead.