An Egyptian protester holds a sign as other demonstrators, said to be members of Egypt's Black Bloc Anarchic group, burn tyres in Cairo. Credit:AFP PHOTO / KHALED KAMEL Professor Ransley said not all Black Bloc protest participants were "super violent". "There's peaceful anarchists as well as violent anarchists," she said. "The challenge for police is to work out which ones are the real danger and which ones simply want to be there." Black Bloc is a loose association of anti-capitalism protesters that began in Europe in the 1980s and operates now more as a tactic against police than as a strict organisation.

Black Bloc protested at Melbourne's 2006 G20 conference, one organiser told security writer Clive Williams from Macquarie University in 2011. "One of the Melbourne demonstration organisers, Mick Armstrong, noted 'I was one of the organisers of the G20 demo from the Stop the War coalition and I am also in Socialist Alternative'," he told Professor Williams. Professor Ransley said Black Bloc commonly protested in Europe, Britain and North America against what it believed were the adverse effects of capitalism after the global financial crisis in the late 2000s. She said they were seen during several of the Occupy protests in North America in recent years. Occupy has raised its profile in south-east Queensland in the past two years, camping in Post Office Square in Brisbane in 2011 as "Occupy Brisbane" before being evicted.

For G20, Occupy Brisbane is working under the banner of the Brisbane Community Action Network-G20 group, going by the name BrisCAN-G20. BrisCAN-G20 is a group of community groups that have organised one large G20 protest march on Saturday, November 15, which leaves Roma Street Forum at 11am. They have also organised a three-day "people's alternative G20", including indigenous, climate change and civil rights speakers from November 12-14, immediately before the G20 leaders' forum. The G20 summit runs from Friday, November 14-16 at the Brisbane Convention and Exhibition Centre. Spokesman Max Riethmuller said Occupy Brisbane doubted that Black Bloc would be coming to Brisbane, but agreed with Professor Ransley that it was naive to rule it out.

"I think it unlikely that Black Bloc will appear for a number of reasons," Mr Riethmuller said. "We are not ruling it out, however. "But there has been a softening in the anti-global agenda in recent times and we've also heard that Black Bloc aren't interested because it is too far away and it is not worth the investment in time and energy." He said, though, that these were just rumours. "We think that is possible that they will turn up. It is certainly naive to say that it is not possible," Mr Riethmuller said.

He said Occupy Brisbane and BrisCAN-G20 were interested only in putting an alternative to the G20 world leaders' summit. "We are not out there to cause trouble," he said. "We would rather stimulate a positive debate - and in terms of the march – we want to get people questioning the existing paradigm. "But we don't want to replace it with one that is just as violent." He said if Black Bloc protesters appeared it would be a matter for police.

"We just want to have our say. If other people turn up and cause trouble, then it is between them and the authorities." Police say 21 protest groups have registered to demonstrate at the G20 leaders' forum. Assistant Commissioner Katarina Carroll, who heads the Queensland Police G20 Group, said while they had been given the heads-up on 21 protests, more clandestine protests were likely. "I definitely expect that and, for those groups, we're purposely reaching out to them," she said. "...But I do expect, like any major event, that there will be some groups that are unknown to us until very late in the day."

Ms Carroll said police were aware of protests planned up to a week before the November 15-16 summit. Loading She said enhanced police powers were already in place through amendments to the G20 (Safety and Security) Act, which was passed in State Parliament last October. - with Cameron Atfield