The city is in lockdown mode. A 5km concrete and steel security barrier snakes around a large chunk of the central business district, cutting off the Opera House and Circular Quay from the public.

The 3-metre-high barrier has been nicknamed 'The Great Wall of Sydney' or the 'Rabble-Proof Fence' by locals, after the 2002 Australian film Rabbit-Proof Fence.

Armed police are buzzing around Darling Harbour on jet skis, patrolling the skies in helicopters and trooping around the streets in large squads, dressed in combat boots and blue jumpsuits.

The city - or Fortress Sydney, as it's been dubbed - ground to a halt following the arrival of US President George W. Bush on Tuesday. He had just made a lightning visit to Iraq.

'From the green zone of Baghdad to the green zone of Sydney,' said Antoinette Abboud, from the left-wing group Union Aid Abroad. She was speaking at the Alternative Media Centre, a facility set up by half a dozen non-governmental organisations in a trades union hall in Chinatown to provide a critical view of the official Apec agenda. Among the centre's guests this week was Matt Howard, a former US marine who did two tours of duty in Iraq but now believes that the war is immoral and wrong.

'The authorities have shut down the city of Sydney - what are they afraid of?' Mr Howard, 26, asked. 'Freedom of speech and assembly are what we are supposedly trying to instil in Iraq and yet they've been taken away on the streets of your own city.'

Australia handles these big events extremely well - the 2000 Olympic Games and the 2003 Rugby World Cup went off without a hitch. But Australian efficiency can sometimes turn into officiousness.

Earlier this week a group of German tourists who casually snapped a few pictures of the security fence were astonished to be told by police that they would have to delete the images from their cameras. And a march yesterday by school students in protest at the war in Iraq was much smaller than expected because the state government and police had warned that they would deal 'severely' with any children caught playing truant.

The city's patience has been sorely tested by traffic jams, roadblocks and police checkpoints. While traffic backs up outside the security fence, inside the protected zone businesses are hurting.

'It's been very quiet - my takings are down by more than 50 per cent,' said Shan Zhang, 34, originally from Guangzhou and now the owner of a newspaper kiosk in Circular Quay.

'They shouldn't have put up the fence - it makes the city look ugly and it's not necessary.' The area is normally thronged with tourists, but yesterday visitors were outnumbered by seagulls and police.

'Closing down the city just for George Bush is pathetic,' said Helen Lopez, 27, as she sat in traffic in the city centre. 'I work at the airport and when Bush flew in last night [Tuesday] people found it really hard to get home because of all the road closures.'

But others have welcomed Apec and feel that far from sulking, Sydney should be celebrating.

'It's a good way of showcasing the city to the world,' a commuter said. 'Plus I'm looking forward to the extra public holiday we get on Friday.'