TOKYO - China and other Asian countries could end up at war over territorial disputes if governments keep up their "provocative behaviour", US Defence Secretary Leon Panetta said Sunday.

Speaking to reporters before arriving in Tokyo on a trip to Asia, Panetta appealed for restraint amid mounting tensions over territorial rights in the East China Sea and the South China Sea.

"I am concerned that when these countries engage in provocations of one kind or another over these various islands, that it raises the possibility that a misjudgment on one side or the other could result in violence, and could result in conflict," Panetta said, when asked about a clash between Japan and China.

"And that conflict would then have the potential of expanding."

The Pentagon chief's trip coincides with an escalating row between Asia's two largest economies over an archipelago in the East China Sea administered by Tokyo under the name Senkaku and claimed by China under the name Diaoyu.

Tensions have steadily mounted since pro-Beijing activists were arrested and deported after landing on one of the islands in August. Japanese nationalists then followed, raising their flag on the same island days later.

On Tuesday, Japan announced it had nationalised three of the islands in the chain, triggering protests in China. Tokyo already owns another and leases the fifth.

Thousands of anti-Japanese demonstrators mounted protests in cities across China.

It also showed footage of more than 1,000 protesters burning Japanese flags in nearby Guangzhou and storming a hotel next to the Japanese consulate. Chinese state media reported a turnout of more than 10,000 in the city.

Japan's Prime Minister Yoshihiko Noda called on China to ensure the safety of Japanese citizens and businesses after widespread protests on Saturday saw attacks on individuals, establishments and Japanese-built cars.

"This situation is a great disappointment and so we are protesting" to China, he told Fuji Television.

Panetta said he and US Secretary of State Hillary Clinton "both strongly urge that these countries - rather than engaging in that provocative behaviour - engage in an effort to find ways to peacefully resolve these kind of issues."

Panetta, who is due to hold talks on Monday with his Japanese counterpart before heading to China, predicted economic rivalry would lead to more feuds in the future over potentially resource-rich areas in the Asia-Pacific region.

"We're going to face more of this. Countries are searching for resources," he said, adding: "There's got to be a peaceful way to resolve these issues."

"What we don't want is to have any kind of provocative behaviour on the part of China or anybody else result in conflict."

Territorial disputes in the South China Sea also have Washington worried, as China has refused to withdraw claims to virtually all of the strategic waterway and has been accused of bullying smaller states in the area.

Meanwhile, the newly-appointed Japanese envoy to China died in a Tokyo hospital Sunday, officials said, ruling out any link to growing anti-Japan protests in Chinese cities over an escalating territorial row.

Shinichi Nishimiya, who was officially appointed on Tuesday, was taken to hospital after falling ill on a street near his home in the capital's fashionable Shibuya district on Thursday, according to reports.

"Ambassador Shinichi Nishimiya died in a hospital", the foreign ministry said in a statement. The death had "nothing to do with any accident or anti-Japanese demonstrations" in China, a foreign ministry official told AFP.

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