By Michelle Price and Christine Kim

Three days after a landmark stock trading scheme linking mainland China and Hong Kong missed its launch date, top officials from either side declined to offer a new timeline, adding to pressure on Beijing to contrive a solution.

The stock connect scheme, a key milestone in the liberalization of China's capital markets, is aimed at allowing global investors to trade China shares via Hong Kong for the first time, while giving mainland investors access to Hong Kong-listed stocks, was set to go live on Monday.

But in a surprise move on Sunday, Charles Li, Chief Executive of Hong Kong Exchanges and Clearing Ltd, said it had not received regulatory approval but was unable to say why, or when it might get the green light.

Ashley Alder, Chief Executive of the Hong Kong Securities and Futures Commission, said on Wednesday his agency had completed all regulatory steps needed for the launch of the scheme.

This was the first time the Hong Kong regulator spoke on the subject since the scheme, widely expected to go live on Oct. 27, was suddenly delayed by what investors believe was failure by Beijing to address tax and other operational issues.

Speaking at the Thomson Reuters 5th Pan-Asian Regulatory Summit, Alder said he hoped trading through the key scheme would start in the "not too distant future," without elaborating.

The trading scheme was due to be launched at a time when Hong Kong is grappling with a pro-democracy protest that is now entering its second month and has at times, seen protesters clashing with police.

Separately, Bo Que, executive vice-president of the Shanghai Stock Exchange, said he was not aware when the scheme might start up. "We are just waiting. It is entirely up to the regulators at this moment and we have no idea when it will happen," he told Reuters on the sidelines of a World Federation of Exchanges event in Seoul. "The Shanghai Stock Exchange, Hong Kong Stock Exchange - we've already done our jobs."

Market professionals speaking at a Reuters China Summit this week said resolving the capital gains tax issue was critical for the link to go live, the timing of which was ultimately a political decision for Beijing.

Hong Kong does not charge capital gains tax, but China levies 10 percent, as well as a 5.6 percent tax on business profits, and it is not clear how gains would be treated under the proposed scheme.