Failure to properly handle sensitive issues between the US and China could "very likely disturb and undermine" their military-to-military relations, a top Chinese official told US National Security Advisor Susan Rice Monday.

Rice is the highest-level US official to visit the capital since an international tribunal this month rejected China's vast territorial claims in the South China Sea -- infuriating Beijing and fuelling tensions with Washington.

Her trip is intended to prepare for a visit by President Barack Obama to a G20 summit in the city of Hangzhou in September.

The Permanent Court of Arbitration in The Hague on July 12 denied the legal basis for Beijing's claim to nearly all of the sea, parts of which are also claimed by neighbouring nations.

In recent months Washington has sent naval vessels close to reefs and outcrops claimed by Beijing to assert the principle of freedom of navigation, sparking anger in China which has built a series of artificial islands in the area capable of supporting military operations.

President Xi Jinping told Rice at a meeting Monday that China was "strongly committed" to building good relations with the US based upon the ideas of "no conflict, no confrontation, mutual respect and win-win cooperation".

But at an earlier encounter with Rice, top Chinese official Fan Changlong, vice chairman of the Central Military Commission warned that ties between the two powers could easily fray.

"We should be honest with ourselves that deep down in this relationship we're still faced with obstacles and challenges," he said, adding that military ties had been "impacted by some complicated and some sensitive factors".

"If we do not properly handle these factors it will very likely disturb and undermine this steady momentum of our military-to-military relationship," he warned.

Rice noted that "risks of unintended consequences" of the two countries' forces operating in ever-closer proximity had been reduced thanks to better communication and other confidence-building measures.

But despite progress, "we have challenges and differences to discuss and to manage", she said.

In conversation with Xi, Rice stated that the US viewed its relationship with China as "the most consequential in the world today".

"We view China's success as being in America's interest, given our growing interdependence," she said.

China rejected the tribunal ruling on the South China Sea as "waste paper" and asserted its right, if it chooses, to establish an Air Defence Identification Zone controlling flights over the area.

At a regional summit in Vientiane Monday Southeast Asian nations avoided rebuking Beijing or mentioning the ruling, in a joint statement seen as a victory for China.

Rice made no direct mention of the tribunal verdict. But the topic nonetheless looms large over her four-day trip, which also includes a stop in Shanghai to meet business leaders.