Two prominent Hong Kong democracy campaigners on Wednesday urged Western powers to speak out against what they described as Beijing's growing interference in the semi-autonomous financial hub.

On a visit to Washington, Martin Lee, a founder of the opposition Democratic Party, recalled that the United States and other nations had tried to reassure Hong Kong residents by throwing their support behind the deal in which Britain returned the city to China in 1997.

"Every government that supported the joint declaration and continues to support it owes a moral obligation to the people of Hong Kong to speak out when something like today is going terribly wrong," Lee said at the US-funded National Endowment for Democracy.

"All we are asking for is fair play. After all, China promised democracy to Hong Kong."

China has promised to allow direct elections for Hong Kong's chief executive in 2017 but critics question the credibility of the vote if Beijing approves candidates.

Anson Chan, the former number two in the Hong Kong government, said that China needed to permit a "genuine choice" when determining eligibility for the election.

"It's not acceptable to say, 'I don't happen to like what you say or I simply don't like your face,'" she told the forum.

Chan credited the US consul general in Hong Kong, Clifford Hart, for speaking out but she and Lee both accused Britain of reticence.

"To the British government, unfortunately, Hong Kong is an embarrassment to their China trade. Money talks," Lee said.

Lee voiced alarm over media freedom in Hong Kong, pointing to assaults on journalists including the former editor of the liberal Ming Pao, who was critically wounded.

Lee also accused businesses of succumbing to pressure from Beijing not to advertize in critical media.

Business people believe that "if they bow, they give respect, they are going to have more business. But once you bow, they expect you to kneel down, and once you kneel down, they expect you to kneel down and kowtow," Lee said.

Beijing once described Lee as a "running dog of the colonialists" and has pointed out that Hong Kong did not elect its own leaders under British rule.