China's top securities watchdog on Friday downgraded the regulatory rating of several major securities brokerages including CITIC Securities Co, a move that will likely restrain the firms from engaging in riskier business.

CITIC Securities, the country's largest securities firm, was downgraded from AA to BBB rating for the first time in eight years, according to the regulator.

At least six other large securities firms including Haitong Securities Co, Guosen Securities Co and Huatai Securities Co have also been downgraded to a BBB rating.

Deng Ge, a spokesman for the China Securities Regulatory Commission, said that the annual regulatory rating is a comprehensive valuation of securities firms based on their competitiveness, risk management capability and regulation compliance.

"The regulator will use the rating results to adopt a targeted and differentiated regulatory approach on different firms," he said.

The rating cut came after the regulator launched a fresh round of investigations into the securities firms for violations of regulations and laws since the stock market rout of last year.

Analysts at global rating agency Moody's Investors Service Inc said earlier that the downgrade of CITIC Securities' regulatory rating could negatively affect the credit rating of the firm.

Moody's put CITIC Securities on the watch list for a credit downgrade in September following the announcement that several senior executives of the firm had been under investigation for alleged insider trading and information leaking.

Some industry experts warned that the rating downgrade would affect the liquidity of the securities firms as it may increase their financing cost. It could also restrain them from conducting riskier and innovative businesses, as they will face stricter inspection.

The CSRC evaluated a total of 95 securities firms. More than half (54 percent) of them were given B-class ratings while 38 percent of them were granted the A-class rating, according to the regulator. No securities firms were given the top AAA rating.