Anti-Japan protests in China over a bitter territorial row died down on Wednesday as authorities apparently sought to ease tensions on the ground, although political leaders maintained their rhetoric.

There were no crowds outside the Japanese embassy in Beijing -- the scene of mass demonstrations at the weekend and on Tuesday -- and it said police had told citizens to avoid the area.

Armed police remained stationed outside the compound, but the road was re-opened to traffic, effectively preventing any substantial gathering. Other than minor demonstrations outside the consulate in Shanghai, there were no reports of protests elsewhere in China.

The row centres on islands in the East China Sea known as Senkaku in Japan and Diaoyu in China.

They are controlled by Tokyo but claimed by Beijing and Taipei, and tensions peaked after the Japanese government bought three of them from their private owners.

Several days of protests, some of them violent, raised international concerns and fears of conflict between two of the world's top three economies, with Japanese firms shutting or scaling back production in China.

But in a statement posted online the Japanese embassy said Beijing police had sent out text messages in effect telling citizens to "not carry out demonstrations at the embassy and also to cooperate with relevant authorities to maintain good traffic and social order".

The Beijing police bureau did not comment when contacted by AFP.

Police forces across the country posted on their Weibo pages that anyone who committed criminal damage during protests would be arrested, but did not specifically say that demonstrations were banned.

Reports said work at Japanese-owned plants and shops was returning to normal, although some were due to remain closed.

Nonetheless China's vice-president Xi Jinping described Japan's purchase of the islands as a farce in a meeting with visiting US Defense Secretary Leon Panetta, state media said.

He urged Japan to "rein in its behaviour and stop any words and acts that undermine China's sovereignty and territorial integrity", Xinhua reported.

UN leader Ban Ki-moon called for leaders to use next week's annual UN summit in New York to try to calm the dispute.

"Looking at what is happening in the relationship between China and Japan over this territorial issue, I am increasingly troubled by rising tensions in the region," he said in his first comment on the issue.

A foreign ministry spokesman in Beijing blamed the protests on Tokyo's actions, but called for calm among people expressing their "strong and just call" to resist Japanese "infringement" of Chinese sovereignty.

"We maintain that the public express their appeals in a sensible and orderly manner, within the limits of law," Hong Lei said.

China's commerce ministry spokesman Shen Danyang told reporters at a regular briefing: "Chinese laws protect the legal rights and interests of foreign-invested companies.

"Foreign companies, if attacked by illegal actions, should report this to the relevant authorities."

But he warned that the row would "definitely affect the normal development of China-Japan trade and economic relations", without going into specifics.

Around the islands themselves, Chinese state television reported that more than 20 fishing boats from Zhejiang province were within 60 nautical miles (111 kilometres) of the islands, with the closest 68 kilometres away. They were escorted by two fisheries patrol vessels, it added.

The Japan Coast Guard said it was monitoring 14 Chinese ships -- 10 marine surveillance ships and four fisheries patrol boats -- nearby, with the Asahi Shimbun newspaper reporting Tokyo had deployed around 50 vessels.

US Defense Secretary Leon Panetta, who had earlier warned of the risk of conflict over the islands, said during a visit to Beijing he was "confident" that both sides were "concerned with finding ways to resolve these issues".

"We cannot live in the past. We have to live in the future," he said in response to a question about China's experiences at the hands of Japanese forces in World War II.