Japan has called for calm in the wake of a reported decision by China to suspend top-level ties over a territorial row.
A government spokesman said Japan had not yet been formally informed of the move, but urged China to act prudently.
On Sunday, Chinese media said ministerial and provincial-level contacts had been suspended.
It followed Japan's decision to extend the detention of the captain of a Chinese trawler accused of hitting two Japanese vessels in waters both claim. He will be held in detention for at least another week
Japan has a further 10 days to either charge or release the captain. The fishing boat's 14 Chinese crew were released last week.
The incident on 7 September happened near uninhabited islands known as Senkaku in Japan and Diaoyu in China.
The BBC reports the islands, which lie north of Taiwan and south of Japan's Okinawa prefecture, have rich fishing grounds and may have oil and gas deposits.
On Sunday, a statement from China's foreign ministry read on state television said the decision to keep the captain in detention had "seriously damaged Sino-Japan bilateral exchanges".
"We demand Japan return the Chinese captain unconditionally and immediately," it said.
"If Japan continues to take the wrong course, China will take strong counter-measures and Japan will have to take all the consequences," the statement said.
