US President George W Bush has arrived in Sydney amid the tightest security Australia's biggest city has ever seen.
Mr Bush arrived at Sydney airport on Tuesday evening
Air Force One touched down late on Tuesday evening, following Mr Bush's surprise detour to Iraq.
Sydney residents had been told to steer clear of the city centre and main roads were shut for Mr Bush's motorcade.
The city is in virtual lock-down as world leaders gather for the high-profile Asia-Pacific Economic Co-operation forum (Apec) this week.
A 5km (three mile) barrier has been erected across the city's central business district to protect the 21 leaders attending the summit, and more than 5,000 police and troops are patrolling the streets.
Police have been seeking court action to prevent a major protest due to take place on Saturday.
Mr Bush is one of the first leaders to arrive in Australia for the forum. Apec leaders are due to gather formally on Saturday.
Over the coming days, Mr Bush is expected to hold a series of bilateral meetings with Asia-Pacific leaders, including Australia's John Howard and China's Hu Jintao.
Climate change, trade and regional security are believed to be high on the agenda, analysts say.
President Hu arrived in Australia on Monday, beginning his visit with a tour of the state of Western Australia, which is a major exporter of commodities to China.
Mr Hu is due to fly to the capital Canberra before moving on to Sydney later in the week.
Members of the spiritual movement Falun Gong, which is banned in China, are planning to hold vigils during Mr Hu's tour to highlight alleged human rights abuses back home.
Australia's security forces are braced for possibly violent protests over the coming days, having launched the largest security operation the country has ever seen.
Parts of Sydney's rail network will be closed, along with many roads, for much of the week.
The fence, through the city's central business district, is aimed at keeping protesters well away from Apec venues, including the Sydney Opera House, where the summit will take place.
The first Apec protest was held on Tuesday evening, hours before President Bush landed.
Some 150 people gathered in Sydney's Railway Square, shouting opposition to the US president and the war in Iraq.
The police have gone to court over a major rally planned for Saturday, which organisers of the so-called Stop Bush Coalition say could attract some 5,000 people.
The authorities have objected to the planned route, but the case has been adjourned to Wednesday to give the protesters more time to prepare their case.