Beijing's declaration of an air defence zone in the East China Sea kick-started a diplomatic free-for-all yesterday.
Japanese Prime Minister Shinzo Abe told parliament that Beijing's move "was a profoundly dangerous act that may cause unintended consequences".
He added: "Japan will ask China to restrain itself while we continue co-operating with the international community."
China and Japan each summoned the other's ambassador, while South Korea also waded into the row.
And he United States joined ally Japan in vowing not to recognise China’s declaration of an air defence zone, a move that escalated tensions even further.
US President Barack Obama’s administration has vowed to defend Japan and said that the islands - known as the Senkakus in Japanese and the Diaoyus in Chinese - fall under the US security treaty with its ally, which has been officially pacifist since World War II.
“This announcement from the Chinese government was unnecessarily inflammatory,” White House deputy spokesman Josh Earnest told reporters aboard Air Force One.
“There are regional disputes in that part of the world and those disputes should be resolved diplomatically,” he said.
The US military, which stations more than 70,000 troops in Japan and South Korea, said it would not abide by the “destabilizing” Chinese-imposed zone.
“When we fly into this aerial zone, we will not register a flight plan, we will not identify our transponder, our radio frequency and our logo. Those are the four things the Chinese have publicly said are a requirement,” Pentagon spokesman Colonel Steve Warren told reporters.
“We will not in any way change how we conduct our operations as a result of this new policy,” he said.
Beijing announced on Saturday it had established an Air Defence Identification Zone (ADIZ).
It requires aircraft flying over an area of the East China Sea to comply with its orders. Tokyo called in Beijing's ambassador Cheng Yonghua and insisted the plan be withdrawn.
But the appeal received short shrift from Cheng, who said Tokyo should retract its "unreasonable demand".
Cheng's opposite number in Beijing was also carpeted and told that Japan should not make "irresponsible remarks" about the ADIZ.
China published co-ordinates for the zone at the weekend.
The area covers most of the East China Sea and the skies over the Diaoyu Islands - called the Senkakus in Japan - at the centre of a long-running row between Beijing and Tokyo.
The area also includes waters claimed by Taiwan and South Korea, which both expressed concern at the move.
South Korea's Defence Ministry said it would raise the issue with Beijing this week.
Part of the zone overlaps South Korea's own air defence zone and incorporates a disputed South Korean-controlled rock, known as Ieodo, which has long been a source of diplomatic tension with Beijing.
Defence Ministry spokesman Kim Min-seok said: "I would like to say once again that we have unchanging territorial control over Ieodo."
In Taipei, the government pledged to "defend its sovereignty over the archipelago".
Under the rules, aircraft are expected to provide their flight plan and clearly mark their nationality.
They are also expected to maintain two-way radio communication, allowing them to "respond in a timely and accurate manner" to inquiries, the Defence Ministry said in Beijing.
Observers said the zone raised the risk of a miscalculation or a crash that could quickly escalate into conflict.
François Godement, director of the Asia and China programme at the European Council on Foreign Relations, said it would fuel tensions with Tokyo over the Diaoyus.
"China [now] controls the rhythm of its escalation, since it can choose to enforce the ADIZ, or not to enforce it, or to enforce it selectively," Godement said.
Watch: China air defence zone to 'protect sovereignty': govt spokesman
Tetsuo Kotani, a research fellow at the Japan Institute of International Affairs, said Beijing's announcement could lead to a mounting crisis.
"If China implements this, it is likely that Japanese and Chinese fighters will frequently encounter in the overlapping zone.
"The worst scenario is a collision that could escalate into a larger-scale armed conflict if managed badly," Kotani said.
But scholar Liu Jiangyong , an expert in Sino-Japanese affairs at Tsinghua University, said the setting up of the air zone did not immediately translate into a looming conflict.
"I think media are overreacting," Liu said.
The Defence Ministry in Beijing said it had lodged formal protests with the US and Japanese embassies after they criticised the air defence zone.
The ministry said the criticism was unfounded and irresponsible. It also called on the US to stop taking sides in the row with Japan over the Diaoyus.
Defence Ministry spokesman Yang Yujun said: "We reiterate that the purpose of China's approach is to defend national sovereignty and territorial airspace security, maintain the order of airspace flight and is an effective exercise of our right of self-defence."
Strong words from all corners
The East China Sea dispute has simmered for decades but heated up in September last year when Japan nationalized three of the islands, in what it billed as an attempt to avoid a more inflammatory step by a nationalist politician.
Asia’s two largest economies now play an almost permanent game of cat and mouse in the area, with official ships and aircraft shadowing each other.
Newspapers in China, where Japan is often portrayed as the villain due to its occupation in the early 20th century, rejected Tokyo’s outrage.
“Tokyo is hypocritical and impudent in its complaint with Beijing,” said an editorial in the Global Times newspaper, which is close to China’s ruling Communist Party.
“If Japan sends warplanes to ‘intercept’ China’s jet fighters, Beijing’s armed forces will be bound to adopt defensive emergency measures,” it said.
Patrick Cronin, an expert on Asia at the Center for a New American Security, said that China was hoping to set off the “natural proclivities” of both the conservative Abe and the left-leaning Obama.
“China is taunting Japan to act in an incendiary manner while pressing the United States to exercise caution and restrain its ally,” Cronin wrote in an essay.
China, which has rapidly expanded its military as its economy soared over the past two decades, also has territorial feuds with other neighbours including the Philippines and Vietnam.
China’s declaration of the air zone angered South Korea, which has tense relations with Japan linked to historical memories and just days ago had upset Tokyo by cooperating with China to erect a statue of a Korean activist who assassinated a Japanese governor in 1909.
Part of the air zone overlaps South Korea’s own air defence area and incorporates a disputed, submerged South Korean-controlled rock - known as Ieodo - that has long been a sore point with Beijing.
Agence France-Presse, Reuters