During the G20 Summit, the government has decided that the area in the red zone is a semi no go zone. Travel through this area will be restricted and heavily enforced. In a smaller area in this zone you better hope you have proper clearance to enter the security restricted zone.
Being a red zone makes it sound more like a large red light district, though in this case, a district for corrupt politicians to work out how to screw over the public and take away more rights and freedoms. Past summits have shown the tendencies for over policing and arrests being made to hold any citizen that ventures too near for the period of the summit.
I can understand that in general it would be a security nightmare in securing the safety of the various leaders attending the summit. No government holding these summits wants anything to happen to any of the leaders in their own country, so security would be at the maximum alertness throughout the period.
During this period it will be a chargeable offence to carry various items, unless you can prove purchased them and heading straight home. Things like kites are another item that is restricted in the inner restricted zones, amongst the normal every day items are things like flour,eggs and other throw-able items of food etc.
If you have a r/c plane/helicopter think twice about flying it anywhere around this area, you could end up facing time in a cell during the rest of the summit at minimal.