The websites of at least 19 Japanese public and other institutions, including banks and universities, have come under cyberattack since Japan nationalized the Senkaku Islands, also claimed by China, on Sept. 11, the National Police Agency said Wednesday.

The cyber-attacks made it impossible for computer users to access the websites at least temporarily, while some of the attackers tampered with their contents, the NPA said.

An NPA official said the attacks appear to have originated in China, judging from the fact that more than half of the 19 sites had been named as the objects of cyberattacks on the message boards of Chinese hacking groups or on major Chinese chat sites.

The Tokyo Institute of Technology said the website of the university's Center for the Study of World Civilization have come under attack, causing personal data on 1,068 people who had taken part in the center's events to be leaked. The data included the participants' names and telephone numbers.