BEIJING, Sept. 3 (Xinhua) -- China's smaller Shenzhen bourse has warned investors of bubbles behind the soaring profits of its main board market.

    By the end of August, 487 out of the 488 listed companies on the main board of the Shenzhen stock exchange had released their interim reports, with combined net profits standing at 47.5 billion yuan (6.25 billion U.S. dollars), almost double those recorded at the same period last year.

    The Shenzhen stock exchange, which is only less than one third of the Shanghai bourse in terms of market capitalization, has a total of 632 listed companies.

    "Although listed companies achieved rapid growth, investors should still beware of hidden bubbles behind the profit surge and invest in a prudent and rational manner," said the report released on Sunday.

    According to the report, the interim profit figures relied too much on yield of investment in the securities market and the prospects of a continued profit increase is doubtful.

    The contribution ratio of business revenue to profit fell 27 percent year-on-year while that of investment yields to profit soared 50 percent, said the report.

    Meanwhile, the corporate shares index grew much faster than the business revenue and net profit.

    The main-board shares in the Shenzhen market were valued at 42 times the earnings. U.S. investment bank Goldman Sachs earlier warned that if the price/earnings ratio exceeds 25 times, share prices are over-valued.

    Besides, 138 companies saw lower half-year profits compared with the same period last year and another 100 are still in red, the report said.

    China's stock market rose to a new high on Monday, with the benchmark Shanghai Composite Index up 1.96 percent to close at 5,321.06 points, and the smaller Shenzhen Component Index rose 1.63 percent, or 291.93 points, to end the day at 18,164.04 points.

    The continued rise of the market has aroused concern among the securities regulators, who have been striving to maintain stability.

    The China Securities Regulatory Commission (CSRC), the country's securities market watchdog, has announced the conclusion of a three-year comprehensive overhaul of the country's securities dealers to reduce operation risks.

    Shang Fulin, head of CSRC, said that 19 companies were shut down and several others had their business licenses suspended. He said 104 securities companies in operation nationwide were up to standard.

    Vice President Xi Xiaoming of the Supreme People's Court of China was quoted by Caijing Magazine on Monday as saying that law makers were deliberating upon the revision of the Securities Law, requiring those who engage in insider trading and price rigging to bear civil responsibility, such as returning properties or paying a penal sum.

    Although related judicial interpretation is still being drawn up, courts at various levels can still receive such cases.