The Shenzhen stock exchange on Friday used new suspension rules to halt trading in Guilin Sanjin Pharmaceutical and Zhejiang Wanma Cable, China's first two initial public offerings in 10 months, after they rose more than 20 per cent on their debut.

The Shenzhen exhange, which hosts mostly small- and medium-sized companies, adopted rules earlier this month aimed at preventing the wild fluctuations in new share prices which were common in China's IPO boom of 2007. The exchange said it would suspend trading in IPO shares for 30 minutes if prices rise or fall 20 per cent, and for another 30 minutes if they gain or lose a further 50 per cent.

The two listings are being closely watched because they are expected to test the success of new listing rules from China's securities market regulator, the CSRC, which last month rewrote listing rules to ensure that IPOs are more realistically priced — and less like a guaranteed lottery ticket, with startling first-day premiums for investors.