Inner Mongolia Mengdian Huaneng Thermal Power (SHA:600863) said it experienced an abnormal stock movement over three consecutive trading days, but its operations are still normal, according to a Shanghai bourse filing on Tuesday.
Huaneng's closing price between May 28 and June 1 was 46.94%, exceeding the growth of the bourse's threshold.
The company said it has no significant announcement or undisclosed information that could have affected its stock price.
The Chinese power company's shares slumped 6% during Tuesday's midday trade.