Shares of newly listed companies trading on the board for small- and medium-sized enterprises will be suspended for 15 minutes if prices rise or fall by more than 50 percent from opening levels, said the Shenzhen Stock Exchange in a statement. Stocks will be halted again for 15 minutes if price changes exceed 90 percent after trading resumes, it said.

"The main purpose is to curb speculative trading," said Chen Shide, who manages a US$212 million small-capitalization fund at GF Fund Management Co in Guangzhou. "Given the size, companies trading on the growth board are more easily subject to manipulation."

The exchange was prompted to introduce the trading limits, which take effect immediately, after shares of some companies, such as China CAMC Engineering Co, surged to almost triple the opening price on the first day of trading. The government lifted a yearlong ban on stock offerings in May.

China CAMC, the first company to sell shares in an initial public offering since the ban was lifted, had an intraday high that was almost triple its opening price when it debuted in Shenzhen on June 19. The stock's closing price was more than quadruple the offer price. The surge prompted the exchange to initiate an investigation into possible price rigging.

The exchange will also issue a risk warning if 80 percent of the shares in a company change hands on the day they debut, according to the statement posted on its website. The shares won't be suspended in the last 10 minutes of trading and all suspensions will end within the last three minutes before the market closes, it said. The Shenzhen exchange set up the growth board in 2004 to facilitate financing by the country's smaller companies.

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