Asked about the low turnout, Robert Chow Yung, spokesperson for the alliance said the figure was not important. He said he believed more people were prepared to attend the afternoon March.

“Some of those who joined the run said they were so cheeful when running in such as good weather,” Chow added.

This afternoon's march marks the end of the Alliance for Peace and Democracy's month-long signature campaign. More than 1.4 million have signed its petition, the alliance said, beating the 800,000 who voted in Occupy Central's reform poll in June.

Former chief executive Tung Chee-hwa, now a Chinese People's Political Consultative Committee vice-chairman, yesterday became the first state-level leader to sign the petition.

Turnout today will be closely watched to gauge the level of opposition to the plan by democracy advocates to block streets in the business hub if voters do not get a range of candidates in the 2017 chief executive election.

The marchers will also be under scrutiny amid rumours some businesses have pressured staff to take part and that inducements such as free meals have been used to lure participants.

Stanley Ng Chau-pei, president of the Federation of Trade Unions and a spokesman for the alliance, predicted a turnout of 120,000 people. They will gather in Victoria Park this afternoon and head for Chater Garden in Central - the route of the annual July 1 pro-democracy march.

"We are for democracy, too," alliance spokesman Robert Chow Yung said. "But we believe it can be achieved in a peaceful and lawful way."

He dismissed reports that bosses were forcing staff to march and that mainland tourists were being mobilised to participate, describing the rumours as low-level smears.

Two teams of University of Hong Kong researchers, led by polling guru Dr Robert Chung Ting-yiu and sociologist Professor Paul Yip Siu-fai, have accepted the alliance's invitation to help measure attendance.

Turnout has long been a point of contention at pan-democrat rallies. For example, the organiser of the July 1 march, the Civil Human Rights Front, put turnout at over 500,000. Police said there were 98,600, while a team led by Chung put it at up to 172,000.

Today's activities begin with a morning run on the march route. From 9am to 9pm, there will be a "flower for peace and democracy" event in which people are asked to present a flower to show support for peace. There will also be live music in Central.

The campaign was given a boost yesterday when Tung, target of the city's biggest protest since the handover in 2003, signed up. He said Hongkongers wanted a "prosperous and peaceful" city and should "work together" for universal suffrage.

Labour Secretary Matthew Cheung Kin-chung said he had also followed Chief Executive Leung Chun-ying and a host of other top officials in signing.

Ng said there were no plans to make public the signature forms the alliance had collected, citing privacy concerns.

Critics had accused the alliance of being too lax in preventing multiple signatures, as well as accepting signatures from children and non-residents.

"When we organised the signature campaign, we only asked people to sign to support our cause. We did not say that we would hand over their forms to others," Ng said.

He said it was too early to decide what the alliance would do next. "In the area of labour issues, there will still be disagreement among us, the unions, and the big bosses," Ng said.

But Brave Chan Yung, a spokesman for the march's organising committee, said: "The end of the campaign is not the end of the alliance.

"We shall be here and we shall remain prepared to fight the Occupy Central campaign. We will not stop unless the pan-democrats stop their campaign."

The march comes amid debate over the 2017 chief executive election. The poll is due to be held by universal suffrage, but democracy supporters fear the nomination process will "screen out" candidates critical of Beijing. Beijing is expected to set a framework for reform this month.