Thousands are expected to gather for a pro-democracy march in Hong Kong Wednesday but organisers say numbers will be lower than in previous years as momentum has waned since a key vote last month.

It is the first large-scale protest since pan-democratic lawmakers vetoed a divisive Beijing-backed electoral reform package on how the city's next leader should be chosen in June.

The bill was derided by the opposition as "fake democracy" as it stuck to a ruling from Beijing that candidates for the leadership must be vetted by a loyalist committee.

That ruling sparked mass rallies at the end of last year that brought parts of the city to a standstill.

Surging discontent over Beijing's election restrictions led to a massive turnout at last year's July 1 march, with organisers saying a record 510,000 came.

The date marks the anniversary of the handover of Hong Kong to China by Britain in 1997 and the annual march is traditionally an outpouring of protest directed at both China's communist government and the local leadership.

"Everyone anticipates a lower turnout than last year... because the momentum has slowed down after the veto over political reform," said Johnson Yeung of organisers the Civil Human Rights Front.

But Yeung insisted numbers were not important and that this year's march was a chance to reshape the democracy movement's message, which has splintered since the end of the mass street rallies in December.

"Right now people are asking 'what next?' after the veto. We hope the march can set the political agenda and give citizens a chance to discuss how to bring the democratic movement forward."

The march will go from the city's Victoria Park to the government complex where a rally will be held.

Hong Kong is at a political stalemate, with fragmentation in both the pro-democracy and pro-Beijing camps.

Student groups who united for the mass protests have since gone their separate ways and young campaigners are increasingly critical of the path taken by mainstream pro-democracy lawmakers.

Some support a newly emerging "localist" stance that semi-autonomous Hong Kong should seek increasing independence from Beijing, rather than campaigning for democracy in China.

The pro-establishment side was left in disarray after a chaotic vote on the election package which saw the majority of the lawmakers supposed to back the bill staging a mistimed walkout, meaning just eight votes were cast in its favour.

"With the electoral package denied, people are looking for new solutions, and at this stage, nobody has been able to propose a credible way out," political analyst Willy Lam told AFP.

"The most important thing they (the people on the march) need to demonstrate to the Hong Kong public is that the pan-democrats are united."

But Lam said younger campaigners may stay away from the traditional marches.

"It has become fashionable for young people in particular to show that they are not mimicking the clarion call of the senior legislators... they want to show the world that they think independently."