At least 19 Japanese Web sites, including a government ministry and hospital, have been affected by cyberattacks reportedly originating from China, according to Japan's National Police Association (NPA).
In a statement Wednesday, NPA said 300 Japanese organizations were listed as targets on the message board of China's Honker hacker group, while up to 4,000 people posted messages about planned attacks and tools on Chinese chat site "YY Chat".
NPA confirmed 11 Web sites, which included Statistics Bureau of Japan and the government's Internet TV, were difficult to access. Eight Web sites including a Japanese court and Tohoku University Hospital were hacked and displayed images of the Chinese flag as well as text claiming the Senkaku Island belonged to China.
NPA's Cyber Force Center has increased its monitoring of online message boards and chat sites to watch for planned cyberattacks on Japan. It is also working with the Cabinet Secretariat to warn organizations listed as potential targets.
The agency is investigating affected and defaced Web sites to gain more information on the attacks, it added.
The two countries have been in a territorial dispute involving islands in East China Sea but events escalated recently when Japan purchased some privately-owned islands.