The Japanese government formally protested the entry of an armed Chinese government ship and two other vessels into waters that Japan claims as its own on Saturday, according to an official in the Japanese ministry of foreign affairs. This is the first time that an armed Chinese vessel has intruded into the areas that Japan claims as its territory, the official said.

The vessel was formerly a People’s Liberation Army Navy ship and is now operated by another department, according to the official, who asked not to be identified, citing government policy. The ship is armed with an auto-cannon, although the main armament has been removed, the official said.

The three vessels approached waters north of Kuba Island from around 8.19am local time, entering Japanese territorial waters starting from 9.30am and left by 10.50am, according to emailed coast guard statements. The armed vessel was the same one that the coast guard reported on 22 December was sailing in waters 28km east-north-east of one of the islands, according to a coast guard official, who asked not to be named, citing government policy.

Kuba Island is among East China Sea islands whose sovereignty is disputed by Japan and China. Ships from both nations have been tailing one another in the area since Japan bought three of the uninhabited islands from a private owner in 2012. The dispute is among the biggest diplomatic issues between the two nations. The islands are known as Senkaku in Japanese and Diaoyu in Chinese.

Repeated incursions

The Japanese government protested to the Chinese embassy in Tokyo and to China’s ministry of foreign affairs in Beijing, according to the foreign affairs ministry official. The entry of the three ships on Saturday was the 139th time that Chinese government vessels have entered Japan’s waters since September 2012, the official said.

When Japan’s coast guard warned the Chinese to leave its territorial waters Saturday, they responded by saying that the Japanese vessel was in Chinese waters and should leave immediately, Kyodo reported. This is the 35th time this year that vessels of the Chinese government have entered Japan’s territorial waters, according to Kyodo.

Japan’s cabinet approved a record defence budget on 24 December amid China’s increasing military activity in the region.

Increased defence spending

The 5.1 trillion yen ($42 billion) package is an increase of 1.5% from the current fiscal year ending March, marking the fourth straight annual gain under the administration of Prime Minister Shinzo Abe. It accounts for just over 5% of the overall 96.7 trillion yen budget for next fiscal year, also approved on 24 December.

While Abe has denied Japan will send maritime forces to back up US navigation exercises in the South China Sea, he’s said he supports the freedom-of-navigation operations that are challenging China’s claims to one of the world’s busiest waterways. Bloomberg

Andy Sharp contributed to this story.