Chinese Web users flooded to a trendy art zone cafe on Wednesday to celebrate a last-minute halt to a rollout of government-sponsored filtering software, and make a stand for freedom of expression in the Communist-run state.

Dressed in t-shirts mocking the Green Dam program, about 200 Beijing residents had arrived by mid-morning to eat a traditional Chinese breakfast, denounce censorship and prepare for a day-long party.

Originally conceived as part of an Internet boycott to mark the July 1 launch of the filter -- and to give a Web-addicted generation something to do during the 24 hours of offline -- the atmosphere was festive as guests celebrated what many said was an unexpected victory against state censorship.

This is a very rare example for the government to suddenly push back an important decision the night before it is due to be rolled out, said outspoken artist Ai Weiwei, who organised the boycott and the party.

Beijing made a surprising about-face late on Tuesday, hours before an edict that all personal computers sold in China must be preloaded with the program was due to come into force.

The Ministry of Industry and Information Technology said the launch would be postponed and did not give a new deadline.

Officials had said the software was intended to stamp out Internet pornography. But it was assailed by activists, industry groups and foreign officials as politically intrusive, technically flawed and commercially unfair.

We are very happy because we got what we wanted, said Liu Yaohua, a 27-year-old artist. We wanted to express our attitude to Green Dam.

There was trepidation among some party-goers about attending an event that was a direct, if light-hearted, rebuke to a government wary of public challenges to its control.

I am a little bit nervous, but I felt it was very important that I find the strength to come, said painter Zang Yi.

The plan might now drift into oblivion if Beijing decides it does not want to face a second round of pressure from overseas and at home.

At a Beijing mall which specializes in computers and software, vendors shrugged at the news of the climbdown.

It's a piece of software like any other. You can take it out if you don't want it. It's no big deal, said Zhang Bo, standing in front of a row of Chinese-made laptops.

But a lawyer who campaigned against the software warned it was premature to declare victory.

It has not been canceled, just put back, so it's possible that after a certain amount of time it will be pushed back out, said Liu Xiaoyuan, who wants the government to explain why a software ostensibly designed to protect a minority of users -- children and teen-agers -- must be installed on all computers.

Artist Ai said battles over censorship would continue, but the government may have shot itself in the foot with Green Dam, by galvanising young Web users.

When young people who grew up in the 1980s and 1990s found that the computers, which are so vital to their life, might be affected, it very naturally caused a kind of politicization.

(Additional reporting by Ben Blanchard; editing by Benjamin Kang Lim)