Mr Wang's appointment has been reported in the Japanese press, but it has not been confirmed by Beijing.

Tokyo has complained to Beijing about the construction of a drilling facility in the East China Sea, close to what Japan sees as the line separating their exclusive economic zones.

The central government draws the line according to where the continental shelf ends, giving China a much larger area.

Competition between the two powers for energy resources and clashes over demarcating territorial waters had made the confrontation inevitable, said Gao Hong , director of Japanese studies at the Chinese Academy of Social Sciences.

For the past two decades, Beijing has proposed co-operating with Japan in developing resources in the East China Sea while temporarily putting aside territorial disputes.

Japan has not responded to the offer, but insisted that China share geological information and results of test drilling.

Soaring oil prices this year again directed attention to the potentially rich underwater gas field. The issue was set to take priority in relations, along with demands for compensation by victims of chemical weapons abandoned by Japanese troops following the second world war, Professor Gao said.

Relations between the two countries have been bumpy recently, characterised by close trade and economic ties but frosty political interaction. The reduction in Japan's Official Development Assistance loans to China was another sign of frayed bilateral economic relations that awaited repair by the new ambassador.

Leaders of the two nations stopped exchanging visits in April 2001 after Japanese Prime Minister Junichiro Koizumi visited the Yasukuni shrine, which honours war dead including convicted war criminals.