China Haitong Securities is under investigation by the country's stock watchdog for alleged violation of securities regulations, two people with direct knowledge of the matter told Reuters on Friday.
The scrutiny follows probes into CITIC Securities and Guosen Securities, two of China's largest brokers.
Haitong declined to comment, saying there will be a statement after the stock market closes on Friday. Trading in Haitong's shares was halted this morning.
Calls and emails to the China Securities Regulatory Commission were not immediately answered.