Chinese internet stocks have dived in New York trading after the US Justice Department said it was considering launching a fraud investigation.
The news was disclosed by Robert Khuzami, director of enforcement at the US financial services regulator.
Youku, which models itself on web video firm Youtube, was among the hardest hit, falling 18%.
Chinese search engine firm Baidu fell 9%, rival portal site Sohu lost 5.3%, and messaging firm Sina dipped 9.5%.
The fraud concerns have arisen after accounting irregularities emerged at a number of Chinese firms whose shares are traded in the US.