The Queensland premier has defended extraordinary new police powers for the G20 summit, saying he won't stand for meaningless destruction and violence.

Campbell Newman says civil libertarians are right to question the powers, which will let police arrest and detain anyone deemed a threat without giving them bail for at least the week of the summit.

He says he wouldn't be comfortable with those sorts of powers remaining beyond the summit, but they're needed for the duration of the event in November next year.

"These laws will only be brought in for G20 and they expire when the G20 is over," Mr Newman said.

"They're not the sort of laws I'd be comfortable with for normal circumstances.

"What we don't want is the scenes that have blighted other cities such as Toronto, where there was completely unnecessary and just meaningless violence and destruction and vandalism."

He said his government was asked to bring in the powers in the context of joint commonwealth-state planning for the summit.

Mr Newman said they were about having an answer to an influx of organised demonstrators "who come to these sorts of things with hammers, ball bearings, sling slots, all sorts of nasties ... setting out to smash shop windows, injure police, and disrupt a very important meeting of world leaders".

"We're not going to let that happen," he said.

Peter Shields, from the Queensland Law Society, said the G20 Safety and Security Bill now before state parliament enshrines police powers that are drastic and a breach of basic rights.

"It is a bill which has not been properly thought through and there are going to be innocent members of the public who will find themselves in custody," he told the ABC.

Criminal lawyer Bill Potts says for the period of the summit, the normal rights that citizens expect will be "suspended and abrogated in the most draconian way".

"The legislation, for example, makes it an offence to be in possession of prohibited items," he told the ABC.

"That can include eggs, cans of baked beans, model cars, model aircraft and all sorts of things which may be used as projectiles even though they have a simple and ordinary use."