Anti-Japanese feeling is running high in China.
Beijing has suspended top-level ties with Tokyo, flexing its muscles in a growing diplomatic row.
Japan’s treatment of a trawler captain has sparked street protests in several Chinese cities.
Chinese national Zhan Qixiong, 41, was arrested earlier this month over a collision with two Japanese coastguard ships. Now a court in Japan has extended his detention for up to 10 days.
His crew has been allowed home to China. But Beijing remains furious over the captain’s fate.
It has warned of strong countermeasures, in addition to halting talks on increasing flights to and from Japan, and postponing a meeting over coal.
The Japanese control the uninhabited Senkaku islands in the East China Sea. Also claimed by China where they are known as Diaoyu, they lie in a rich fishing area with potentially valuable oil and gas reserves.