China's leaders told US Secretary of State Hillary Clinton during "very good discussions" last week in Beijing that they wanted to pursue a code of conduct with the ASEAN bloc on the South China Sea, Ambassador Gary Locke said.

"I've also heard from many prominent Chinese academics that China would like somehow to return to the status quo, that they would like to lower the temperature," Locke said at the Carnegie Endowment for International Peace in Washington.

Locke said the United States did not take positions on claims but wanted to make sure that no side "engages in any type of activity that escalates tensions and jeopardizes safety and freedom of navigation, which would hurt everybody."

Tensions have soared between China and Japan over a dispute in the potentially resource-rich East China Sea as Tokyo announced that it would nationalize islands where rival nationalists have sailed to stake claims.

In the South China Sea, the Philippines and Vietnam have accused China of a wave of intimidation against fishermen and rival nations' ships as Beijing exerts its claims to virtually all of the strategic waterway.

"It's going to be incumbent upon China and the Philippines to have their own negotiations on this (and) China and Vietnam on a bilateral basis," Locke said.

Locke's remarks, made in passing in response to a question, appeared to take a different emphasis from other senior US officials who have called on China to negotiate with the full 10-member Association of Southeast Asian Nations.

Under a 2002 agreement, China agreed to reach a code of conduct for the South China Sea with ASEAN but Beijing has since preferred to deal with each nation individually, instead of as a unified bloc.

Clinton visited ASEAN's headquarters in Jakarta to urge unity before her talks in Beijing, where Foreign Minister Yang Jiechi said China wanted the "eventual adoption of a code of conduct" on the "basis of consensus."

US officials say that a code of conduct would provide ways to manage disputes and increase dialogue so that incidents do not turn into full-fledged conflicts in the sea, through which half of the world's cargo flows.

Shinichi Nishimiya, who was officially appointed on Tuesday, collapsed on the street near his home in the fashionable Shibuya district of the Japanese capital, Jiji Press reported.

Kyodo News reported that the ambassador was unconscious.

An official at the foreign ministry confirmed Nishimiya, 60, had been taken ill.

"We learned that ambassador Nishimiya was hospitalised this morning for poor health, but don't have any more details," he told AFP.

The official added that he was not aware of any accident.

Jiji press, citing an unnamed government source, said foul play was not suspected.

The Sankei Shimbun said a passer-by who saw the ambassador stumble and fall on a Tokyo street made an emergency call to police.

He was clad in a business suit, the Sankei said, citing an unnamed police source.

Nishimiya, a career diplomat, replaces Uichiro Niwa at a time Japan and China are at loggerheads over a disputed island chain in the East China Sea.

Niwa, a former businessman, raised hackles at home earlier this year when he said a plan by Tokyo's nationalist governor to buy the islands could cause a crisis between China and Japan, jeopardising economic ties.

Nishimiya's appointment came on the day the government in Tokyo said it had finalised the purchase of three islands in a chain it administers under the name Senkaku, but which are claimed by China as Diaoyu.

Anti-Japan protesters rally in Beijing
Beijing (AFP) Sept 13, 2012 - Hundreds of protesters gathered outside the Japanese embassy in Beijing on Thursday, singing the Chinese national anthem and waving flags, to condemn Tokyo's purchase of a disputed island chain.

The latest demonstration came after the Japanese government this week nationalised three islands in a chain it administers and refers to as Senkaku, but which are claimed by China, where they are known as Diaoyu.

"Japan through illegal methods has forcibly occupied our country's territory... this is the behaviour of a thief," demonstrator Xu Xiaolei told AFP.

Police watched as small groups of demonstrators entered Japanese restaurants to shout that the islands belonged to China.

Protests in China are often swiftly dispersed by authorities, but in some cases they are allowed to proceed.

More than 20 cities have seen anti-Japanese protests in the past month and the car of the Japanese ambassador to China was targeted in Beijing when a man ripped the flag off the vehicle.

China dispatched two patrol ships to the archipelago to "assert its sovereignty" on Tuesday.

The territorial dispute has since dominated Chinese media, with state television and all major dailies highlighting Beijing's condemnation of Tokyo's acquisition.

At least one Chinese travel agency said it was no longer accepting bookings for trips to Japan.

"State sovereignty comes above everything," the Sichuan Kanghui International Tour Company said in a statement posted online on Wednesday announcing the suspension of group bookings.

Chinese Premier Wen Jiabao said Wednesday that Beijing would "never yield an inch" over the disputed islands, state-run news agency Xinhua reported.

On Thursday it quoted China's commerce vice minister saying the purchase would "inevitably" have a negative impact on trade ties.

"If Chinese consumers, in a reasonable manner, express their positions and views against Japan's violation of China's territorial sovereignty, I think it is within their rights to do so and it is understandable," Jiang Zengwei said.