The Tokyo-administered islands, known as the Diaoyu in China and Senkaku in Japan, have long been a sore point between the neighbours.

On Sunday, Japan said it observed four Chinese coast guard vessels sailing in the "contiguous" zone, referring to a 12-nautical-mile band that extends beyond Japan's territorial waters.

Last year, Chinese vessels sailed near the Tokyo-administered island chain a record 355 times, including for a period of 215 consecutive days, a Japanese coast guard spokesman told AFP.

Japanese officials regularly protest the presence of the Chinese coast guard and other vessels in the waters surrounding the remote, disputed islands.

Relations between Japan and China were strained by Tokyo's decision to "nationalise" some of the islands in 2012.

On Friday, Japan's coast guard and its US and Filipino counterparts staged joint training drills off Japan's southwest shore -- the second time the countries' coast guards have held training drills together, and the first in Japan.

Territorial disputes with China have pushed Japan to forge deeper ties with the Philippines and the United States.

Earlier this month, Tokyo and Beijing traded barbs over close encounters between their military planes over the Pacific high seas.