The newly appointed Japanese envoy to China died in a Tokyo hospital on Sunday, officials said, ruling out any link to growing anti-Japan protests in Chinese cities over an escalating territorial row.
Shinichi Nishimiya, who was officially appointed on Tuesday, was taken to hospital after falling ill on a street near his home in the capital's fashionable Shibuya district on Thursday, according to reports.
"Ambassador Shinichi Nishimiya died in a hospital," the foreign ministry said in a statement.
The death had "nothing to do with any accident or anti-Japanese demonstrations" in China, a foreign ministry official told AFP.
Nishimiya, a career diplomat, was to replace Uichiro Niwa at a time Japan and China are at loggerheads over a disputed island chain in the East China Sea.
Hundreds of protesters gathered outside Japan's embassy in Beijing on Sunday, throwing water bottles and chanting anti-Japanese slogans, a day after angry demonstrators tried to storm the building.
Niwa raised hackles at home when he said a plan by Tokyo's nationalist governor to buy the islands could cause a crisis between China and Japan, jeopardising economic ties.
Japan insists there is no territorial dispute over islands it administers and calls Senkaku, but which China claims under the name Diaoyu.
Nishimiya had planned to leave for Beijing in October. The government is now considering a replacement from among retired foreign ministry officials, local reports said.