The reality of what life will be like during the G20 has hit home as Brisbane's inner city woke up to find police with greater search powers and fences erected around G20 venues.

Special legislation came into effect today, turning parts of the city from Bowen Hills to Kangaroo Point and South Brisbane and Woolloongabba into official "declared areas".

Fencing around the Brisbane Convention and Exhibition Centre (BCEC), which became a "restricted area" at the beginning of the month, was also erected overnight.

Deputy Commissioner Ross Barnett said it was "incredibly normal".

"People will see from what's going on... this is how how we anticipate it will be for most of next week and leading up to and including next weekend," he said.

"People coming into this precinct as they do every other Saturday and Sunday and enjoying the many opportunities, cultural events that are available - we want that to continue through next week and next weekend.

"We want to encourage people to come into the city and make the most of this unique opportunity."

Declared areas are described in the G20 (Safety and Security) Act 2013 as "an invisible barrier around event and accommodation venues".

They are the areas directly outside deemed restricted areas, such as the BCEC, which have some sort of fencing or physical barrier.

Restricted areas are only accessible to people with a genuine reason to access the area and official accreditation from the G20 Taskforce.

Household items now prohibited without "lawful excuse"

While declared areas are accessible to the public, police have greater powers in those zones, including the power to search people if it is "reasonably suspected" that they are carrying prohibited items such as eggs and glass jars without a "lawful excuse".

Deputy Commissioner Barnett said a commonsense approach would be taken and there must be an identified safety risk for an arrest to be made.

"There's got to be a connection between the item and some intent to possibly disrupt the event or hurt some person," he said.

"The item of itself is not strictly the issue, it's the time, date and place that it's carried and the intent of the person who has it.

"They will use professional judgment and deal with each situation on its merits."

The legislation provides three types of searches, basic, frisk and specific, which, if necessary, involves the removal of clothing.

Other parts of Brisbane will be deemed declared zones this week.

All will stay in effect up to and including Monday November 17.