About 200 US soldiers have arrived in northern Australia, beginning a six-month deployment that marks the beginning of closer co-operation between the allies and a deepened US military presence on the shores of the southern Pacific.
The arrival of the US Marines on Wednesday at their base on the outskirts of Darwin follows agreement between Washington and Canberra to establish a permanent joint-training hub there, with eventual numbers of US soldiers set to rise to 2,500 within five years.
In November, the US and Australia announced plans to send more US military aircraft to Australia to better protect US interests across Asia.
Julia Gillard, the Australian prime minister, said in a statement that the initial six-month rotation would not include heavy equipment, vehicles or aircraft.
"There are no US military bases in Australia, and this will not change," she said.
But, the move has sparked concern in China, where officials have questioned whether it is part of a larger US strategy aimed at encircling it and thwarting the country's rise as a global power.
Jeffrey Bleich, the US ambassador to Australia, said at the welcoming ceremony on Wednesday that the Asia-Pacific region was the "most dynamic area in the world''.
"This is the fastest growing economic area and also the one that is enduring the greatest demographic change and we want to make sure that it continues to be a peaceful, prosperous and stable area," he said.
"We don't see China or India as a threat"
- Stephen Smith, Australian defence minister
"The way that we accomplish that is by ensuring that trade routes are open and that we're prepared for any issue that could come up," he added.
Stephen Smith, the Australian defence minister, speaking to the Marines on Wednesday at the army barracks, called the occasion a historic day in the 61-year-old alliance between Australia and the US.
He rejected analysis that closer military ties between Australia and the US were a response to the growing military assertiveness of China, Australia's most important trading partner.
"We don't see China or India as a threat," he said. "There is nothing inconsistent with our relationship with China and our long-standing, successful alliance with the United States.
"The world needs to essentially come to grips with the rise of China, the rise of India, the move of strategic and political
and economic influence to our part of the world," he said.
The tropical port of Darwin is 820km from Indonesia, allowing soldiers there to respond quickly to any humanitarian and security problems in Southeast Asia, where tensions have risen due to disputes over sovereignty in the South China Sea.
When the deployment was announced last November, US President Barack Obama said: "The notion that we fear China is mistaken. The notion that we are looking to exclude China is mistaken .... we welcome a rising, peaceful China."