China's Shanghai and Shenzhen stock exchanges issued on Sunday the new rules of regulating their member securities companies in a bid to ward off risks in stock trading.

The rules, which will come into effect on May 1, set limits to the varieties, methods and scales of stock trading that dealers are allowed to conduct, preventing them from engaging in high-risk business beyond their capacity.

The securities companies are required to remind their clients of possible risks when being entrusted with abnormal dealings, according the rules.

They can refuse commissions that are likely to seriously disorder the market and report them to the stock exchanges, the rules said.

In specific trading business, the securities companies must sign agreements with their clients on the duties to reveal possible investment risks, according to the rules.

Meanwhile, senior managers of the securities companies can be recognized as "unsuitable candidates" for management positions in the business by national securities watchdog, once they receive disciplinary punishment for three times in their companies' irregular operations.

The new rules will replace previous provisional rules that have been in operation since 1998 and only apply to domestic securities companies with membership in the stock exchanges.

Under the new rules, the Shanghai Stock Exchange will no longer expand its membership, which now stands at 151, while the Shenzhen bourse, which has 175 member securities companies, will limit the total number of members.

The new rules came at a time when talk of a bubble has been rife in the Chinese stock market, raising government and public concern.

The benchmark Shanghai Composite Index gained 130 percent last year and had jumped nearly 10 percent in January alone before a recent correction took it back to about where it started the year.

Despite a bullish stock market, the government has warned investors of illegal securities companies, which usually involve swindling clients of funds with claims of high returns.

On Feb. 12, the State Council approved the China Securities Regulatory Commission would lead a inter-ministerial team to crack down on illegal securities business.