The United States' top naval commander in Asia described military relations with China as "collegial" on Tuesday and rejected Cold War comparisons, urging "methodical and thoughtful" diplomacy in the region.

Vice Admiral Scott Swift, commander of the Japan-based US 7th Fleet and in Sydney for bilateral exercises, said maritime security was an increasingly important issue in the Indo-Pacific region as both trade and militarisation boomed.

"Economic power is being converted to military power in many parts of the region, which may increase the temptation to use coercion or force in an attempt to resolve differences between nations," he said in a speech to the Lowy Institute foreign policy think-tank.

"The rising of the seas and the opening of the (Arctic's) Northern Passage will bring new security challenges that must be dealt with as well," he added, speaking of global warming's impact in the region.

Swift said he was "very encouraged by the pace" of military connections in the region amid escalating tensions over issues including the South China Sea.

China claims nearly all of the sea, rejecting competing claims to parts of it by the Philippines, Vietnam, Brunei, Malaysia and Taiwan.

Some of the claimants have expressed concern at Beijing's increasingly assertive military and diplomatic tactics to stress its control.

US President Barack Obama warned China last week against using force or intimidation in its maritime disputes and urged a peaceful resolution.

Swift said his focus was on inclusive military operations, seeking "to the maximum extent possible multilateral exercises", adding he had had "very collegial exchanges with PLAN (Chinese navy) ships throughout the region, and really throughout the world".

"We need to be methodical and thoughtful about the process by which we pull the relationships together," he said.

"In the past I think there's been a rush to achieve a form of success without fully understanding what success is, especially in the context of the parties that are coming together."

Swift said he believed military collaboration with China was "bringing us closer" to a naval understanding similar to that which existed between the US and the Soviet Union to prevent conflict at sea during the Cold War.

But he distanced himself from comparisons with the 40-year US-Soviet standoff, saying there were "very, very different circumstances", starting with the fact that the 7th Fleet was as large as the entire Chinese navy.

"We have much more in common than we do have in competition with China," Swift added.

"The Cold War was really a competition between governments, competition between our militaries, who was the strongest was the question of the day. I just don't see that in today's maritime environment."

Swift said he was "heartened" by the role of the Association of Southeast Asian Nations in the region and welcomed discussions about whether its mandate should extend beyond economic issues.

"The instability that is resident within the South China Sea is really ringed by all those countries that are participants in ASEAN, so its relevance is much higher than what it was even four or five years ago," he said.

"If it grows into a maritime focus more than what it has now, I'd be very anxious to participate in that process."

He said he was "very interested in furthering the code of conduct in the South China Sea", an ASEAN initiative which "has great value".

But if it were to be meaningful there must be agreement on its structure and contents, he said.

China has been reluctant to reach such a code of conduct with the ASEAN bloc, preferring to negotiate individually with each country.

US Secretary of State John Kerry urged progress on the pact at a meeting of Southeast Asian foreign ministers in Brunei this month.