Some of the world's biggest banks and asset managers have asked the Hong Kong securities regulator for more time to prepare for a landmark China stock trading link due to uncertainty over the rules of the scheme, according to a letter seen by Reuters.

The Hong Kong-Shanghai stock connect scheme was widely expected to go live on Oct. 27, but the letter sent on Friday by the influential Asia Securities Industry & Financial Markets Association could delay the debut of trading until late November.

In the letter, ASIFMA said its members could not begin trading next week because of uncertainty surrounding some technical issues and a lack of clarity over taxation. It asked for its members to be given a month's notice before the launch of the Hong Kong-Shanghai link-up.

The letter added that banks would need time to calibrate trading systems and prepare client documentation once the details had been finalised.