Investors in Hong Kong have bet a record amount on exchange-traded funds that profit when stocks decline, showing how quickly sentiment is shifting following a breakneck rally.

A key stock market index in Hong Kong saw the biggest single-day drop since the financial crisis on Tuesday. The Hang Seng index fell by -2172.99 (-9.41 percent) on Tuesday. The drop followed an announcement on Tuesday by China's economic planning agency that outlined details of measures aimed at boosting the economy but refrained from major spending initiatives.

U.S. stocks rebounded Tuesday after falling oil prices released some of the pressure that built up on the market. The S&P 500 rallied 1% to claw back all of its loss from the day before. The Dow Jones Industrial Average rose 126 points,