Japan and China need more sophisticated communication strategies if they are to work through their territorial row, US Vice President Joe Biden said Tuesday as he vowed Washington would stand by Tokyo.

Biden, in Tokyo at the start of a three-nation tour of Asia, said he will be talking "in great specificity" with Chinese leaders about Beijing's sudden declaration last month of an air defence zone, including over islands disputed with Japan.

"We, the United States, are deeply concerned by the attempt to unilaterally change the status quo in the East China Sea," Biden told reporters in a joint press conference with Japanese Prime Minister Shinzo Abe.

"This action has raised regional tension and increased the risk of accidents and miscalculations."

Tensions in the region are at their highest in years, with China and Japan squaring off over a chain of uninhabited islands in a feud that has some observers warning of the danger of an armed confrontation.

The US, bound to Tokyo by a security treaty, is looking on alarmed at the growing chances of limited hostilities between the world's second largest economy and Washington's chief ally in the Asia-Pacific.

Observers say rising China, buoyed by its surging economy, is becoming more confident and the dispute with Japan is part of a larger effort to stamp its authority on a region long dominated by the US.

Nerves are particularly frayed after Beijing's proclamation of an Air Defence Identification Zone (ADIZ), in which it says all aircraft must obey its instructions or risk unspecified "defensive emergency measures".

The move was flatly rejected by the governments of the US, Japan and South Korea.

"This underscores the need for crisis management mechanisms and effective channels of communication between China and Japan to reduce risk of escalation," Biden told reporters.

"I will be raising these concerns in great specificity directly when I meet with the Chinese leadership the day after tomorrow," he said.

And he vowed that the United States, which has a security treaty that compels it to come to Japan's aid if it is attacked militarily, would stand by its ally.

"We will remain steadfast in our alliance's commitment," he said.

Abe has been looking for robust backing over his position that Beijing is being unreasonable and aggressive. He was heartened when US B-52 bombers flew into China's ADIZ just days after it was announced.

"We... confirmed that we should not tolerate the attempt by China to change the status quo unilaterally by force and we will continue to work closely in dealing with the situation based on the strong US-Japan alliance," the Japanese premier said.

"We reaffirmed that policies and measures, including those on operation of Self Defense Forces (Japan's military) and US forces, are not changed and that we will maintain close cooperation."

Beijing's announcement of the ADIZ also provoked anger in Seoul, which, like Tokyo and Washington sent official planes into the zone without notifying China.

The shared reaction in Japan and South Korea marked a rare moment of harmony in a relationship marked by friction over shared history that hobbles US attempts to bring its two chief regional allies together.

"We believe that Northeast Asia will be strongest when its two leading democracies work together to meet common threats, and when the three of us -- the United States, Japan and the Republic of Korea -- work together to advance common interests and values," Biden told the Asahi Shimbun newspaper ahead of his trip.

Some analysts believe the declaration of the zone was a far-sighted move by Beijing in its campaign to undermine Japan's claims to control disputed islands, and ultimately, push the US out of the western Pacific.

Others, however, say it looked more like an over-reach by an administration that did not fully anticipate the vehemence of the reaction.

China's defence ministry spokesman in a statement late Tuesday defended the zone, saying it was in line with international conventions and did not threaten any specific country.

But the 1,000-word statement on the official Xinhua news agency strongly criticised Japanese actions over the disputed islands since September last year.

"Japan's actions have seriously harmed China's legitimate rights and security interests, and undermined the peace and stability in east Asia. China has to take necessary reactions," it said.

Biden will move to Beijing on Wednesday to hold talks with Chinese President Xi Jinping before flying to Seoul, where he is to meet President Park Geun-Hye.