China says it is lodging a formal complaint with Japan after Japanese authorities arrested 14 pro-China activists who landed on an island chain claimed by both countries.

Japanese police say the activists arrived on the islands by boat from Hong Kong Wednesday, despite Japan's heightened security presence in the area. At one point, Japan's coastguard fired water cannons at the Chinese fishing vessel carrying the activists.

Japan accuses the detained of violating immigration law and has sent them to Okinawa to face charges.

The activists say the landing was aimed at countering a plan by a group of Japanese lawmakers to visit the disputed islands.

The uninhabited islands, known as Senkaku in Japanese and Diaoyo in Chinese, are a frequent flashpoint between Tokyo and Beijing. They are located in a gas-rich area and surrounded by rich fishing grounds.

The landing came as tension broke out between Japan and its neighbors on the emotionally charged anniversary of Tokyo's surrender in World War II.

In a separate demonstration, a group of South Koreans reached a set of disputed islands known as Takeshima in Japan and Dokdo in Korea. It comes less than a week after South Korean President Lee Myung-bak visited the island chain, provoking ire in Tokyo.