For international investors accustomed to speed, trading in China's stock market is like flying blind.

That is because everybody who transacts on the Shanghai Stock Exchange gets price updates just once every three seconds, or five seconds if they have a lower level of service.

While the gaps have gone largely unnoticed by individual investors who make up more than 80 percent of the volume, they are presenting a problem for overseas traders－many of whom just recently gained access to Chinese mainland shares through the Shanghai-Hong Kong Exchange link.

Lack of continuous pricing prevents investors from using strategies that rely on speed and precision, a hurdle that has gotten even bigger in recent weeks as volatility in Chinese shares climbed to the most extreme levels worldwide. As the country seeks to raise the profile of its equity markets on the global stage and gain acceptance into MSCI Inc indexes, UBS Group AG said getting prices in three-second snapshots is one of its biggest concerns.

The gap "makes it very difficult for anyone to trade as the data is stale by the time it hits", said Joel Hurewitz, the global head of broker-dealer strategy at Nomura Holdings Inc's Instinet Pacific unit in Hong Kong.

Most developed markets stream continuous share prices to meet the needs of professional investors, who increasingly use fast-moving computer algorithms to buy and sell. As prices move between snapshots, investors in China are left in the dark. "That is actually one of our biggest concerns, specifically in theelectronic trading space with respect to the ability to read, acknowledge and analyze data," said David Rabinowitz, the head of direct execution for Asian equities at UBS.

For arbitrageurs seeking to exploit short-term price differences between dual-listed shares in Shanghai and Hong Kong, the gaps make it difficult to square essentially real-time prices in Hong Kong with the relatively stale information from the mainland. The Hang Seng China AH Premium Index shows valuations are 29 percent more expensive on the mainland.

"Even if you have a fast network between Shanghai and Hong Kong, the market data coming from the mainland and sent overseas is based on snapshots," said Alex Godingen, the head of business development in Asia Pacific at Fidessa Group Plc. This creates a "processing delay", he said.

Shanghai's bourse has to weigh the costs of distributing large amounts of data against the benefits of continuous pricing, according to China Investment Information Services Ltd, a Hong Kong-based unit of the Shanghai Stock Exchange that manages the flow of data from the mainland to Hong Kong. Volumes in Shanghai have surged to all-time highs this year after a record-long bull market in the benchmark index gave way to the biggest rout in many years.

"Real-time streaming data consumes large bandwidth," Man Leung, an assistant manager at CIIS, wrote in an e-mail. "We have to balance the information and bandwidth requirements."

Vendors are expanding bandwidth from the mainland, while Hong Kong banks and brokers are finding ways to adapt. Interactive Data Corp, which disseminates data from the Shanghai exchange, plans to increase capacity after recently doubling it, said Levent Mehmet, vice-president for trading solutions in Asia Pacific at IDC.

Different vendors receive snapshots from Shanghai at different moments, so combining feeds from several sources improves the overview of the market, said Stephane Loiseau, head of cash equities and global execution in Asia-Pacific at Societe Generale SA.