“The ferocious velocity of the first few minutes in China caught some people by surprise,” Rob Bernstone, managing director in equity trading at Credit Suisse, told the WSJ. “Whatever traders were planning to do today as far as 2016—I think those bets went out the window.”

The precipitous selling in Chinese markets, with a 7% plunge in the CSI 300 Index, also triggered a trading halt before the end of the day.

Deutsche X-trackers Harvest CSI 300 China A-Shares ETF

Max Chen contributed to this article.