Australia, the US and Japan have agreed to stronger defence ties and jointly called for a peaceful settlement of maritime disputes in the Asia-Pacific region.
The meeting between Tony Abbott, Barack Obama and Shinzo Abe on the sidelines of the G20 summit came a day after the US President vowed use "every element" of America's power to ensure peace and stability.
Mr Obama also said regional security shouldn't be based on "coercion or intimidation ... where big nations bully the small, but on alliances for mutual security".
By the end of this decade, the US is set to deploy most of its navy and airforce to the region.
The three leaders agreed on Sunday - at their first trilateral meeting since 2007 - to boost joint military exercises.
In the statement, they urged "freedom of navigation and over-flight, and the peaceful resolution of maritime disputes in accordance with international law".
China is in dispute with four South East Asian countries over territories in the South China Sea, and with Japan over another set of islets.
"The three leaders reaffirmed the global reach of their cooperation and the value of comprehensive US engagement in the Asia-Pacific region," the statement said.
A trilateral military exercise is understood to be planned for June 2015 in Queensland.
Australia's interest in Japan as a possible supplier of replacement submarines for the Collins class is also understood to have come up.
Chinese President Xi Jinping will deliver a speech to parliament in Canberra on Monday, where he will outline his vision for the region and commitment to peace and stability.
President Xi has also signalled a closer defence relationship with Australia, which is a major trading partner.
Prime Minister Abbott told the two other leaders at the start of the meeting: "It's good to be here with two such economic and strategic partners."
They also resolved to tackle the spread of Ebola, Islamic State extremists as well as Russia's annexation of Crimea and actions "to destabilise eastern Ukraine".
The first leader-level trilateral dialogue between Australia, the US and Japan took place in Sydney, involving Mr Abe, John Howard and George W Bush.
At a media conference to wrap up the G20 summit in Brisbane, Mr Abbott was asked whether he put a plan to upgrade the fleet before US and Japanese leaders.
The prime minister said it was well known Australia's fleet would need replacing in the medium term future and that the country was in the process of commissioning its next generation of submarine.
"You would expect a country like Australia to have discussions with a number of partners about how this best can be done because we have a duty," Mr Abbott told reporters.
"We have a duty to our country, we have a duty to our friends and partners right around the world to have an effective defence force."
Mr Abbott also stressed that Australia, Japan and the US were full of admiration for China over its "extraordinary" peaceful economic transformation, and that China was the largest customer of all three nations.
"So the point I keep making - I made it in Tokyo, I made it in Seoul, I made it in Beijing, I made it in the parliament, I make it here again - is that when it comes to security we will all advance together or none of us will advance at all," he said.
