China said on Thursday that Tokyo's illegal "island" claims encroach on the high seas and the interests of the international community as a whole.

Chinese Foreign Ministry spokesperson Lu Kang said it is illegal for Japan to claim areas around the Okinotori Atoll as its continental shelf or exclusive economic zone (EEZ).

Lu made the remarks in response to reports that during the G7 summit in Japan later this month participants will discuss maritime order based on international law, and Japan recently reiterated that it classed Okinotori as an island, not a collection of rocks.

Lu explained that the atoll, some 1,700 km south of Tokyo, was a group of rocks in the western Pacific Ocean, and less than 10 square meters of the rocks are above sea level at high tide.

According to Article 121 of the United Nations Convention on the Law of the Sea (UNCLOS), rocks that cannot sustain human habitation or economic life cannot have EEZ or continental shelf status.

Lu reminded that in 2012, the Commission on the Limits of the Continental Shelf did not accept Japanese claims over the geopolitical classification of Okinotori, nor any continental shelf claims.

Japan now claims about 700,000 square kilometers of sea around the atoll, Lu said, noting that such claims encroach on the high seas and ocean floor under international jurisdiction, and damage the interests of the international community as a whole.

According to the UNCLOS, international seabeds and their resources are the commonly inherited property of mankind.

It is unimaginable that Japan should knowingly break the international law and at the same time try to paint itself as an advocate of rule of law in international maritime affairs to win support at the G7 summit, Lu said.

"This only shows that certain countries are frivolous and hypocritical when they are talking of safeguarding international maritime law, and it will be more absurd if any organization will choose to stand for such behavior," Lu said.