Officials from Tokyo conducted a survey on Sunday of three uninhabited islands in the East China Sea which are at the centre of a territorial dispute between Japan and China.
State media in China described the move as illegal.
The team was dispatched to the islands by Tokyo Governor Shintaro Ishihara who wants to buy the islands, which are called Senkaku in Japan and Diaoyu in China.
However, the party did not land on the islands. The Japanese government did not give the group permission to do so.
In July, Prime Minister Yoshihiko Noda said that the government was also negotiating to buy the islands.
Japan administers the islands, but China says the group has been part of Chinese territory since ancient times.
