The supposed meeting place in Beijing in front of McDonald's in the busy Wangfujing shopping district. It is usually packed with tourists and shoppers but the presence of uniformed police and overseas reporters made it difficult to tell who was there for the rally. Hundreds of people ended up milling around in Beijing, and a handful in other city centres, before the gatherings were broken up by police.

The turnout apparently even surprised those who posted the mysterious call online.

'We were pleasantly surprised by the outcome of the February 20 activities,' said an anonymous statement purportedly from the organisers, carried by US-based Boxun.com this week.

Boxun's founder, Watson Meng, says he does not know the identity of the organisers but believes they are from the mainland, judging from the content of their messages.

More postings have since appeared on the website, extending the call to supporters in 23 cities to stage peaceful rallies every Sunday afternoon to demand food, jobs, housing, social justice and political reform.

'Just go for a stroll in all the large and small city centres every Sunday at 2pm. Smile at each other and chat,' another posting said this week. 'China's 'jasmine behavioural art' needs no guns and barrels ... Strolling is people power, smiling is also people power.'

Amid the 'whodunnit' guesses, there is talk that Boxun itself may have been the mastermind, although Meng vehemently denied any such role.

Meng insisted that Boxun, which has since been attacked by hackers, was a neutral platform for news and opinions not tolerated on the mainland and would not proactively engage in political activities. He said shorter versions of the initial call for rallies first appeared on mainland microblogs, QQ (an instant messaging service), and the mainland equivalents of Twitter and Facebook in the middle of last week, before a full version hit his website late last week.

'But whether people paid any attention to it was not our call,' he said.

Unnerved by the rally call, the authorities went on high alert. Tens of thousands of police and security agents were put on standby across the country last Sunday, about 100 activists and rights lawyers were put under various forms of detention before the rallies, and a handful of people who showed up on the day were reportedly detained.

The word 'jasmine' has been censored as a sensitive term on the mainland's most popular internet search engines and microblogging services in the past few days.

Despite the clampdown, supporters said they were interested in joining future rallies. Using sophisticated tools to cross the authorities' firewall, many have been watching out for developments on censored sites such as microblogs, Twitter, Facebook and their local equivalents. 'I would like to witness a historic moment ... when I am old, I can tell my grandchildren proudly that I was there,' said a Twitter user in Beijing who declined to give her name because she feared reprisals.

Analysts say the authorities' reaction shows how jittery they are about the power of the internet and any possible signs of an uprising.

'That shows that they are very, very scared ... As soon as any kind of political call happens anywhere in the world, even if it's not serious like this one, they have to intervene,' said Jean-Philippe Beja, a senior research fellow at the Centre for International Studies and Research at Paris-based Sciences Po.

With additional reporting by Priscilla Jiao, Alice Yan