The China Securities Regulatory Commission said it is probing "a massive sell-off" after Monday's sharp dive in the market.
The CSRC said it had received whistle-blower reports and market monitoring reports, and had organized inspection and enforcement teams.
The Shanghai Composite index lost almost 8.5 percent on Monday, the largest daily loss in eight years, followed by another 1.68 percent loss on Tuesday.
Regulators have previousely said that "malicious short sellers" will be severely punished, and investigations against short selling and market manipulation have been conducted nationwide, according to the Ministry of Pulic Security.
No results of the investgations have been released.
