Two US B-52 bombers flew over a disputed area of the East China Sea without informing Beijing, US officials said Tuesday, challenging China's bid to create an expanded "air defense zone."

The unarmed aircraft took off from Guam on Monday and the flight was previously scheduled as part of a routine exercise in the area, the defense officials said.

"Last night we conducted a training exercise that was long-planned. It involved two aircraft flying from Guam and returning to Guam," Pentagon spokesman Colonel Steven Warren told reporters.

No flight plan was submitted beforehand to the Chinese and the mission went ahead "without incident," Warren said.

The two aircraft spent "less than an hour" in China's unilaterally-declared Air Defense Identification Zone (ADIZ) and did not encounter Chinese planes, he said.

A defense official, speaking on condition of anonymity, confirmed to AFP the two US planes were B-52 bombers.

China announced the expanded air defense zone amid a mounting territorial dispute with Japan over an island chain in the East China Sea known as Senkaku in Japanese and Diaoyu in Chinese.

The area also includes waters claimed by Taiwan and South Korea, which also have both expressed their displeasure at Beijing's move.

Under the rules declared by China, aircraft are expected to provide a flight plan, clearly mark their nationality and maintain two-way radio communication to allow them to respond to identification inquiries from Chinese authorities.

Japan, the United States and several other governments sharply criticized China's announced air defense zone.

Australia summoned Beijing's ambassador to express its opposition and Tokyo called on airlines to refuse to accept China's demands to abide by new rules when flying into the zone.

Pentagon officials said the United States views the area as international air space and American military aircraft would operate in the zone as before without submitting flight plans to China in advance.

The territorial dispute over the islands has simmered for decades but in September 2012, Japan nationalized three of the islands, in what it portrayed as an attempt to avoid a more inflammatory step by a nationalist politician.

Beijing, however, accuses Tokyo of disturbing the status quo, and has sent ships and planes to the islands in a show of force.

In response, Japan has mobilized vessels and aircraft, raising fears the tensions could trigger an accidental clash.

Without taking sides in the territorial feud, UN Secretary General Ban Ki-moon meanwhile called on China and Japan to negotiate an end to their dispute.

Ban on Tuesday said tensions should be handled "amicably through dialogue and negotiations."