Two known troublemakers banned from entering G20 district

Queensland police will start banning people from the G20 summit as soon as special legislation comes into force.

Twenty-four protest groups are planning to attend the event in Brisbane in November.

Special legislation will give police additional powers in specific areas during the summit, mostly around the Brisbane Convention and Exhibition Centre in South Bank, and Brisbane city.

Assistant Commissioner Katarina Carroll says individuals can be banned from attending the event under the legislation.

Known troublemakers have been identified.

"In the next week or two there will be two people on the prohibited persons list, and those people will be firmly served with that paperwork and they will clearly know who they are," she said.

She did not answer questions about the identify of the pair but said that the number of prohibited individuals could grow ahead of the summit.

Assistant Commissioner Katarina Carroll says police will try to talk to protest groups ahead of the summit.

"Some of those groups we've been speaking to for nearly two years and in recent times the other groups that have come on board, we've also been engaging with them," she told reporters in Brisbane.

Ms Carroll warned destructive behaviour won't be tolerated.

"We've been very very clear from the outset that if there is damage, if anyone is hurt, or if there is destruction during the event we will be very swift in our action."

Just over two weeks before the event, associate professor Janet Ransley from the Griffith University School of Criminology and Criminal Justice warned there had been evidence of international groups mobilising, including the black bloc anarchist group.

"Whilst we have information about the black bloc ... I'm certainly not in a position, nor would I explain to you today, whether or not they're coming to the event."