PM 'frank' on South China Sea concerns

Prime Minister Malcolm Turnbull has raised the touchy subject of the South China Sea with his Chinese counterpart, as the US ramps up its military involvement in the region.

The United States has said it will send troops and combat aircraft to the Philippines for regular, more frequent rotations, and will conduct more joint sea and air patrols with Philippine forces in the South China Sea.

The move is set to inflame tensions with China, with the increased US military presence and activities in the region likely to be viewed as a threat.

Mr Turnbull on Friday declined to comment on the US announcement, but insisted he had raised the issue with Chinese Premier Li Keqiang on every occasion the pair had met - including their meeting on Thursday night.

"(We have) a very honest and open relationship as two leaders who can speak to each other candidly and frankly about all of these issues and of course many others as well," Mr Turnbull told reporters in Beijing during his first official visit to China as prime minister.

Mr Turnbull said Australia's clear position was all claimants should settle the disputes peacefully and in accordance with international law.

"The remarkable economic gains in this region, by every country including our own and of course China, has been based on the foundation of peace and stability," he said.

"Anything which has the potential of disturbing that peace and stability works against the interests of all nations."

He dismissed reports Australia's economic relationship with China could be jeopardised by Australia's stance on the issue, insisting China understood Australia's position.

The announcement by US Secretary of Defense Ash Carter in a news conference with his Philippine opposite Voltaire Gazmin, was the first time the US disclosed that its ships had carried out sea patrols with the Philippines in the area.

He insisted that the US did not intend to be provocative and was "trying to tamp down tensions here".

The Chinese Foreign Ministry issued a statement saying military exchanges should not "support a few countries in challenging China's sovereignty and security, inciting regional contradictions and sabotaging regional peace and stability".

The South China Sea is an important trade passage, rich in fishing stocks and believed to be home to extensive oil and gas deposits.

It has been the subject of overlapping claims from several Asian nations as well as complaints about China's building of artificial islands in the area.

Mr Turnbull has previously described China's actions in the disputed waters as "counterproductive".