Last year organisers said 180,000 people crammed into Victoria Park in Causeway Bay with the same demands as previous years - the vindication of those who died in the crackdown and an end to one-party rule and establishment of a democratic China.

While the event has always annoyed mainland officials and Beijing loyalists in Hong Kong, no one expected this year's event to be especially controversial … until the alliance unveiled its slogan for this year's vigil in early April.

Among the online community, the focus on the first part of the slogan - "Love the country, love the people; Hong Kong spirit" - soon overshadowed the rest of the message, which reads: "Vindication of June 4; Never give up".

Horace Chin Wan-kan, the author of a book published two years ago that advocated "city-state" status for Hong Kong, has led an online battle alongside his pro-autonomy followers against the slogan, and the alliance.

Chin, a cultural expert and an assistant professor of Chinese language at Lingnan University, is a vocal supporter of the Hong Kong Autonomy Movement.

The movement has been widely criticised for waving colonial-era flags at protests in the past few months, against the backdrop of intensifying cross-border tension over a range of issues.

In online appeals for Hongkongers to boycott the vigil, Chin argues that the mainland's political system is irrelevant to the city's democratic movement, and that pleading for vindication only serves to "legitimise" Communist Party rule.

"A line must be drawn between Hong Kong and the mainland; and the interests of Hong Kong people must always come first," Chin, who calls himself a "localist", wrote. "The spirit of Hong Kong should never be about loving the country, or the countrymen.

"In those days when Hong Kong people supported the student protests in Beijing, we were free-riding on the hope of a democratic China. For the past 20 years we felt morally indebted to the students who lost their lives … today, we shall realise that Hong Kong's democracy has to rely on its own people."

On Friday the row took a dramatic turn when the alliance dropped the "love the country, love the people" slogan.

A day earlier Ding Zilin, founder of the Tiananmen Mothers' support group whose son was killed in the crackdown, criticised the slogan as stupid and out of sync with mainland people's thinking.

Former Democratic Party lawmaker Cheung Man-kwong, a protégé of late veteran democrat Szeto Wah, was one of the core members of the alliance who stood up last week to defend it.

"Patriotism was the driving force that saw a million Hong Kong people take to the street in 1989, and the city has always been clear to differentiate loving the country from loving the party," he said in an emotionally driven speech ahead of a pre-June 4 march last Sunday.

"The Communist Party has exhausted every attempt in the past to make Hong Kong people forget the June 4 crackdown, but we have responded by candlelight every year to show we refuse to forget."

Cheung insisted that patriotism and democracy always come together.

"It is only wishful thinking that Hong Kong can stay away from the influence of China. We cannot hope for the city's democracy and forget about human rights in China," he said.

The split between supporters of autonomy and leaders of the democratic movement has left many veterans of past vigils with a tough decision to ponder.

Lawmaker Gary Fan Kwok-wai, who has been backing Chin in advocating "local interests" in the face of the cross-border tensions, said he could not convince himself to boycott the vigil.

"I will attend. Political disputes are nothing compared with students who lost their lives in Beijing," said Fan, a member of the NeoDemocrats, a splinter group of the Democratic Party. "To Hongkongers, the call for vindication of June 4 means a lot more than an unattained demand. It is a symbol that [encompasses] our core values."

Agnes Chow Ting, a member of student activist group Scholarism, takes another perspective to avoid the patriotism debate.

"Being present at the vigil is not necessarily related to national identity," she said. "As world citizens, we should show concern about what happens around us every day, regardless of whether it is in China or anywhere else."

The University of Hong Kong's Public Opinion Programme has been conducting polls on public sentiment towards the June 4 crackdown since 1993. Last year, 61 per cent of respondents supported vindication of the democracy movement, the most since the handover. In the same poll, the alliance received a support rating of 54.5 points out of 100, the highest since 1999.

But when asked if Hong Kong people have a responsibility to push for democracy in China, the figures showed a significant decline, with fewer than 70 per cent saying "yes" last year, compared with 83 per cent in 1993.

A survey by Chinese University and HKU pollsters of people who attended the vigil in 2004 showed that 94 per cent saw their presence as a protest against the crackdown by the Communist Party. About 90 per cent said it was to mourn those who lost their lives, and 86 per cent said it was to push China's democracy.

Dixon Sing Ming, a political scientist at the Hong Kong University of Science and Technology, said the intensified cross-border tension in the past few months, together with the recent scandals that challenged the core values of the city, had played a crucial part in this year's controversy.

"Broadly speaking, it is the compassion of Hong Kong people towards the pro-democracy movement in 1989 that drives them to attend the night vigil year after year," he said.

"The younger generation may not feel as strong since they were not direct witnesses. I would not be surprised if there is a stronger call to focus on local interests in the future."

Sing added that Hong Kong people were realistic; only a few of those joining the vigil did so with promoting democracy on the mainland as their main purpose.

"The alliance should be aware that an overemphasis on the political rhetoric of two decades ago could backfire or even lead to cynicism," he said.