Vice-president Joe Biden arrived in Japan on Monday amid a rift with America's closest Pacific ally after China announced an expanded air defense zone.

While the US and Japan have made a public show of unity following China’s demand last week that all aircraft passing over a disputed island chain identify themselves to Beijing, American and Japanese aviation authorities are adopting divergent positions over whether civilian flights should comply with the Chinese demand.

Biden, who arrived in Tokyo late Monday night local time, now has the task of reassuring Japanese and South Korean allies over their fraught confrontation with China about its expansive so-called “air defense identification zone.” The issue is likely to overshadow a week-long trip to the three Asian countries that US officials had hoped would focus on economic affairs.

“I believe this latest incident underscores the need for agreement between China and Japan to establish crisis management and confidence-building measures to lower tensions,” Biden said in an interview with Japan’s Asahi Shimbun newspaper on the eve of his arrival.

The dispute over the Japanese-controlled islands, known as the Senkaku in Japan and the Diaoyu in China, began nine days ago when Beijing unilaterally declared its enlarged air defense identification zone. The Chinese defense ministry ordered all aircraft flying through the zone to notify Chinese authorities, warning that it would it would "identify, monitor, control and react to" any air threats or unidentified flying objects coming from the sea.

Washington has not taken a formal position on the sovereignty of the islands. However, it recognises Tokyo's administrative control, and said explicitly last week that its treaty to defend Japan militarily applies to the islands.

The US, in its most direct challenge to Chinese military endeavors in two decades, flew two B-52 bombers through the zone without notifying the Chinese. The US navy has sent P-8 Poseidon patrol aircraft to Japan, a long-planned move that gives the allies greater ability to track hostile submarines and other naval ships in Japanese waters.

But Washington and Tokyo have appeared out of sync on the appropriate response that civilian aircraft should take to the newly-declared Chinese zone.

Japan’s civilian and commercial aviation companies are defying the Chinese air defense identification zone, declining to give the Chinese prior notification of any passage through the disputed air space. Following Washington’s lead, Tokyo has sent military aircraft, including F-15 fighter jets and Awacs surveillance planes, directly through the claimed Chinese zone. For Japan, which has recently reopened debate on its formal post-second world war pacifist defense policies, it has been a notably aggressive response.

In contrast, the US Federal Aviation Administration instructed aircraft to comply with the Chinese identification demand in the interest of safety, even as US officials insist they do not recognize the legitimacy of China’s air declaration.

The discrepancy has roiled Japan, despite Washington’s repeated insistence last week that its commitment to Japanese security is beyond question. The Japanese TV station NHK quoted a former senior foreign ministry official, Yukia Okimoto, saying the US “hurt Japan’s interests over an issue related directly to Japan’s national security in a way visible to the whole world.”

Shinzo Abe, the Japanese prime minister, said he would “deal with the matter by coordinating closely” with Biden, who will visit Beijing on Wednesday and meet with China’s president Xi Jinping.

The US vice-president’s trip enables him to have face-to-face contact with all the regional players with a stake in the controversy, including South Korea, where he will spend two days meeting senior government officials.

South Korea, which has strained relations with Japan, is also being sucked into the dispute. Local reports indicate that Seoul is in the final stages of expanding its own six-decade-old air defense identification zone southward, which would overlap with territory claimed by China.

The move comes after a defense consultation last week between China and South Korea failed to reassure Seoul that China’s expanded zone was aimed exclusively at Japan.

China’s military is immature by the standards of the US. But the pace of change and increase in military spending in China has been rapid, causing deep concern in the region and in Washington over Chinese intentions, which Biden will seek to test during his talks in Beijing.

The Chinese move, coupled with the evident disparity between American and Japanese responses, has prompted an escalation in a region home to three of the world’s largest economies, further complicating the Obama administration’s message that the US is itself a Pacific power, and one that has an unshakable commitment to the security of its allies.

It is unclear if Biden will attempt to mediate between China, Japan and South Korea. Aides to the vice-president told reporters last week that Biden would seek only “clarity” from China about its military intentions, but declined to say that he would call for China to reverse its declaration, which Japan is seeking.

China has thus far shown no signs of retreating over the zone. It announced that it scrambled its own fighter jets in the air defense identification zone on Friday, an intended challenge to the US and Japan. But the Japanese defense ministry sharply questioned whether the Chinese jets ever actually passed through the zone, issuing a statement saying it spotted no additional air traffic in the area.