Japan has called for calm in the wake of China's apparent decision 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.
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 islands, which lie north of Taiwan and south of Japan's Okinawa prefecture, have rich fishing grounds and may have oil and gas deposits.
A spokesman for the Japanese prime minister told the BBC the government has not been informed officially of China's decision to suspend high-level contacts.
But Noriyuki Shikata said if the reports were true it was "regrettable" and called for calm and prudence from the Chinese side.
On Sunday, a statement from China's foreign ministry read out 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. If Japan continues to take the wrong course, China will take strong counter-measures and Japan will have to take all the consequences," it said.
Meanwhile, a planned visit by 1,000 Japanese students to the Shanghai Expo has already been called off.
The students were scheduled to depart on Tuesday but, said Mr Shikata, late on Sunday China told the Japanese embassy in Beijing that they should not come.
He described the move as "extremely inappropriate".
The BBC's Roland Buerk in Tokyo says the dispute has exacerbated Japanese concerns about the growing power of its Asian rival.
China is eclipsing Japan as the second biggest economy in the world and Japan is becoming increasingly dependant on exports to China, now the country's biggest trading partner, he says.