US-listed Chinese stocks tumbled Thursday after regulators in Beijing and Ant Group denied reports that Jack Ma’s fintech company was dusting off shelved plans for an initial public offering. The Nasdaq Golden Dragon China Index, which tracks major Chinese companies traded on US exchanges, finished the day down 6.8%—worse than the Nasdaq’s 2.75% decline. E-commerce platforms led the sell-off with Ant investor Alibaba Group Holding down more than 8%, JD.com falling 7.6%, and Pinduoduo sinking 9.6%. The three largest Chinese equity exchange-traded funds were all down, led by the internet-focused KWEB finishing the day down 6.7%. The broader MCHI and...