Six Chinese surveillance vessels briefly entered contested waters surrounding islands at the centre of a territorial dispute between China and Japan.
China labelled the infringement as 'law enforcement' and a display of jurisdiction over the islands, with three vessels leaving shortly before the remaining three departed.
The incident occurred after Japan sealed a deal to buy three of the islands, known as Diaoyu in China and Senkaku in Japan, were acquired by the Japanese Government by a private owner from the country earlier this week. Taiwan has also claimed ownership over the resource-rich islands.
The Japanese Coast Guard confirmed that two Chinese ships entered Japanese waters at 6:18am local time on 14 September, followed by a further four ships less than an hour later. Three vessels departed after 90 minutes following warnings, with the remaining three vessels leaving a few hours later.
Japan has responded strongly to the infringement, with local reports alleging Prime Minister Yoshihiko Noda has established a task force to address the issue, while also summoning the Chinese ambassador to officially protest.
Japan chief cabinet secretary Osamu Fujimura said: "We understand that the dispatch of six ships is surely an unprecedented case, considering past incidents."
China responded by confirming the presence of its ships in Japanese waters, stating: "These law enforcement and patrol activities are aimed to demonstrate China's jurisdiction over the Diaoyu Islands and its affiliated islets and ensure the country's maritime interest."
The islands have proven to be at the centre of disputes in the past, with a series of incidents highlighting the issues surrounding contested ownership. In September 2010, a Chinese fishing boat collided with a Japanese Coast Guard vessel, with the fisherman arrested and held in Japanese custody amid vehement protests from China. In July 2012, Taiwanese activists landed on the islands to stake a claim for China's ownership, raising a PRC flag.
Tensions in the region continue to grow as China has taken a harder line with territorial disputes in the region recently, with the US calling for 'cooler heads' in order to maintain the trading relationship between China and Japan. US defense secretary Leon Panetta is visiting the region this weekend, with the row threatening to complicate stronger disputes surrounding oil and gas fields in the East China Sea.