(Updates with new police comments, more detail) By Michael Perry SYDNEY, Sept 1 (Reuters) - Construction of a concrete and wire security fence which will cut the centre of Sydney in half began on Saturday as part of the nation's biggest security operation for next week's Asia-Pacific leaders' summit. The 5-km (3-mile) fence will isolate the leaders, who include U.S. President George W. Bush and Russian President Vladimir Putin, in the Sydney Opera House and surrounding hotels. Thousands of protesters, demonstrating against the Iraq war and global warming, plan to rally in Sydney during the Asia Pacific Economic Co-operation (APEC) meetings. "Right now, there's one priority, there's one show in town and that's APEC," New South Wales (NSW) state police commissioner Andrew Scipione told reporters on Saturday. "APEC must be delivered. It's the biggest security event we've ever had in this nation," said Scipione. Police expect the protests to be violent and have barred 29 known protesters from the centre of Sydney and warned demonstrators not to march near the APEC summit venue. "Our police, particularly in APEC, are not there to be punching bags, they are not there to be spat upon, they are not there to be assaulted," said Scipione. "If people do that, our police will act appropriately, but they will be very decisive, it will be very rapid," he said. While Australian security officials say they have received no intelligence of a terrorist threat to APEC, they have launched the country's biggest ever security operation. Australia's counter-terrorism alert remains unchanged at medium, which means a terrorist attack could occur. Australia, a staunch U.S. ally, has never suffered a major peace-time attack on home soil, although 92 Australians were among more than 220 people killed in bombings on the Indonesian island of Bali in 2002 and 2005. The Australian government has spent A$169 million in the past six years preparing APEC security. A total of 21 leaders are to attend the APEC leaders' meeting on September 8-9, along with spouses, and 5,000 APEC delegates. FORTRESS SYDNEY Many Sydneysiders have criticised APEC security, claiming it will turn Sydney's inner city into a fortress, with people asked for IDs and bag searches. A total of 3,500 police and 1,500 defence force will be patrolling Sydney. A 45-nautical-mile restricted air space will be enforced by fighter aircraft and police helicopters. A navy mine sweeper will patrol Sydney Harbour, along with navy divers, water police and special forces. The city's underground railway network will be closed during the APEC weekend and motorists have been warned to stay out of the city as many roads will be closed. The 2.8-metre (9-ft) high security fence, dubbed by critics as Sydney's "Great Wall of APEC", will cut off the northern part of the central business district. "As people move in and through the city from today, they should leave plenty of time to get to their destination," NSW deputy premier John Watkins said on Saturday. "There will be delays walking and catching public transport especially around the northern part of the city...be prepared for travel to take longer than normal." President Bush has apologised to Sydneysiders for any inconvenience his visit and APEC will cause. "I'm looking forward to the beautiful city and to the extent I inconvenience (Sydneysiders), I apologise," Bush told Australian television in an interview broadcast on Friday.
