Tensions between Asia's two biggest economies reached their highest level in years yesterday when China sent six surveillance ships into the waters around islands at the centre of its territorial dispute with Japan.
The ships' crews exchanged warnings with Japanese coastguard ships as they briefly entered the area around the Diaoyu islands, as they are known in China, which are situated in the East China Sea.
Relations between China and Japan have long been tense, but Tokyo's recent decision to buy the uninhabited islands, known in Japan as the Senkakus, from a private owner has brought anger to the boil in China.
China's state broadcaster CCTV repeatedly played footage of a Chinese marine surveillance officer aboard one of the ships radioing the Japanese vessels, demanding they leave.
"The actions of your ships violate China's sovereignty and rights. Any unilateral act from your side regarding the Diaoyu islands and its affiliated islands is illegal and invalid. Please stop any infringing acts. Otherwise, your side will bear the consequences caused by your actions," the officer said.
"It is deplorable that the invasion of the territorial waters happened and we strongly request that the Chinese authorities leave our territory," Japan's chief cabinet secretary Osamu Fujimura told reporters yesterday.
While the islands are surrounded by rich fishing grounds, they also have strategic importance. The row is also seen as a clash between China's growing regional clout in the face of what it sees as Japanese nationalism and aggression.
China believes the islands were illegally invaded and occupied by the Japanese during the Second World War, and were returned to China when Japan was defeated. Diplomats in Beijing say neither side wants the situation to escalate, but admitted it might be difficult to keep things calm.
Japan has elections coming up, and China is facing a tense change of leadership due next month, both of which make finding a solution that plays to their respective domestic audiences problematic.
Next week is also the anniversary of the Mukden Incident in 1931, when Japan seized Manchuria in northeast China, triggering 14 years of occupation by China. The date is known as 9.18 in China and is likely to see major protests.
Chinese Assistant Foreign Minister Le Yucheng said Japan's actions were like stealing a neighbour's bicycle and said the decision to send the ships to the islands was a "powerful measure" to defend China's sovereignty.