Japan on Sunday backed the United States sailing warships close to disputed land in the South China Sea but said it had no plans to send its own maritime forces to support the operation.

Last month Washington infuriated Beijing when the USS Lassen guided missile destroyer sailed within 12 nautical miles of at least one land formation claimed by China in the disputed Spratly Islands chain.

Chinese authorities monitored and warned away the vessel, but did not otherwise intervene, although Beijing later summoned the US ambassador and denounced what it called a threat to its sovereignty.

Reports last week said Japanese Prime Minister Shinzo Abe told US President Barack Obama on the sidelines of the APEC summit in Manila he would consider sending his country's ships to back up American operations in the area.

But Defence Minister Gen Nakatani played down the suggestion after bilateral meetings with Australian counterpart Marise Payne and Foreign Minister Julie Bishop in Sydney.

"We have actively been trying to contribute to stability in the region but as far as we are concerned there is no plan to be a part of the freedom of navigation operation of the United States," he said.

"At the US-Japan summit (in Manila), I believe Prime Minister Abe conveyed this stance to President Obama."

Foreign Minister Fumio Kishida appeared less decisive, saying "nothing has been decided yet, no decision has been taken".

"The international community must work in concert to respond to the situation," he said, speaking immediately before Nakatani.

"For the US, conducting operations to ensure the freedom of navigation, this is strictly based on international law ... and Japan is supporting the US in this regard."

Tensions have mounted since China transformed reefs in the South China Sea into small islands capable of supporting military facilities, a move the US says threatens freedom of navigation in a region through which one-third of the world's oil passes.

China insists on sovereignty over virtually all the resource-endowed South China Sea, which is also claimed in part by a handful of other countries.

Washington has repeatedly said it does not recognise the Chinese claims.

In a communique after the talks in Sydney, Japan and Australia called on "all claimants to halt large-scale land reclamation, construction, and use for military purposes" in the South China Sea.

They also "urged claimants to exercise restraint, take steps to ease tensions and refrain from provocative actions that could escalate tensions".

Two-thirds of Australian trade passes through the South China Sea and Bishop said freedom of navigation in the area was imperative.

"We have a very deep national interest in maintaining peace and stability in that region," she said.

"We don't take sides on the competing territorial claims in the South China Sea, but we have acknowledged that land reclamation and construction activity that's undertaken by China and other claimants raises tensions in the region.

"We're particularly concerned at the prospect of militarisation of artificial islands and structures."

Philippine leader says 'world is watching' China in sea row
Kuala Lumpur (AFP) Nov 22, 2015 - Philippine President Benigno Aquino told an Asia-Pacific summit on Sunday that "the world is watching" whether China would behave as a responsible power in the simmering standoff over maritime territory.

Aquino kept up a drumbeat of growing criticism of China's expansion of tiny atolls into fully-fledged islands, as leaders including Chinese Premier Li Keqiang met in Malaysia.

The issue has increasingly loomed over the regional diplomatic and security outlook, with China accused of upsetting the status quo by moving to enhance its presence in the South China Sea.

"We are hopeful that China would honour its word and respect the rule of law," Aquino said, according to a copy of his address to the 18-country East Asia Summit in Kuala Lumpur.

Aquino's comment referred specifically to a dispute with China over maritime territory, which Manila is bringing before an international court.

"The world is watching and expects no less from a responsible global leader," Aquino said.

Beijing has vowed not to take part in the case, saying the Permanent Court of Arbitration in the Hague has no jurisdiction over a matter concerning Chinese sovereignty.

Heads of government from 18 countries including the United States, China, India, Russia, Japan and nations in Southeast Asia are meeting for the annual East Asia summit, this year hosted by Malaysia.

A Philippine diplomat confirmed Aquino made the comments in the closed-door meeting.

The Kuala Lumpur diplomatic and political meetings follow a trade-related forum in Manila earlier in the week that included many of the same leaders.

The maritime issue has become the stage for a big-power confrontation between China and the United States, which warns that Beijing's actions could threaten freedom of navigation.

US President Barack Obama, who also attended both summits this week, has called on China to halt its land reclamation.

China has declared ownership of virtually all of the South China Sea, conflicting with the various claims of Vietnam, Malaysia, the Philippines, Taiwan and Brunei.

The Philippines has been the most vocal in challenging China.

Aquino said Beijing's island reclamation was "in total disregard of international law" and its assertiveness had "come to a point wherein we are now no longer allowed to enter areas within our Exclusive Economic Zone".

Manila insists the United Nations Convention on the Law of the Sea, which the Philippines and China have both ratified, should be used to settle the bitter row.

"The great equaliser is the rule of law. Under the rule of law, right prevails over might," he told his fellow leaders.