e city's Hyde Park, after a longer route through the city was banned.

"Two police officers have been injured and one of them will treated in hospital for his injuries," a police spokeswoman told AFP. "We have three people arrested."

The organizers estimated that 10,000 people took part but police put the number at 5,000.

The march was organized by a group called the Stop Bush Coalition, but some demonstrators also expressed their concerns over a range of other issues, including climate change.

As the protesters marched, Bush and 20 other world leaders gathered at Sydney's iconic Opera House on the harbor, some 20 minutes walk away, for the this year's Asia-Pacific Economic Cooperation (APEC) summit.

The leaders, including Australian Prime Minister John Howard, who is a close Bush ally, Russian President Vladimir Putin and Chinese President Hu Jintao, did not catch even a glimpse of the protesters.

The heads of government were protected by a five-kilometer (three-mile) long, three-meter high fence snaking through the city and 5,000 police and soldiers patrolling on land, sea and in the air.

The security operation, the largest ever mounted in Australia, included overflights by air force jets, police on jet skis in Sydney's famous harbor and special laws aimed at cracking down on protesters near the summit.

The protest was colorful, with people beating drums and blowing whistles while others were dressed as polar bears, kangaroos or Britain's Queen Elizabeth II.

As they set off, they chanted: "Howard, Bush, USA, how many kids did you kill today?"

"George Bush is a great evil - he should get out of this country," said one of the protesters, former Guantanamo Bay detainee Mamdouh Habib, who was released without charge in 2005.

Deanna Adam, who attended the protest with her two children, India aged seven and Kyle, eight, told AFP: "We are here because we oppose the war in Iraq. It's costing too many lives. I have children and I am worried about their future."

A large banner carried by a group of marchers read: "War criminals not welcome here - Bush go home".

Half way through route the marchers staged a sit-down protest for about 20 minutes against the police ban on the longer route.

Police had blocked off roads with barricades of converted buses, which could also be used as holding cells for arrested demonstrators.

Senior officers had said they feared a repeat of violent demonstrations seen in Melbourne during the World Economic Forum in 2000 and at last November's G20 economic leaders meeting.

"Police lines will come under attack and a full-scale riot is probable," Chief Superintendent Steven Cullen, the head of the state Public Order and Riot Squad, said this week.

Cullen was speaking at a court action in which police successfully applied for an order that effectively allowed the protesters to march for only two city blocks.