Japan says four Chinese government ships have entered the East China Sea amid the territorial dispute between Tokyo and Beijing over a group of uninhabited islands.Japan’s coast guard said on Saturday that the ships entered the area near the islands, known as Senkaku in Japan and Diaoyu in China, shortly after 9:00 am (0000 GMT). "We are telling them to leave the area," a coastguard spokesman said. China's State Oceanic Administration (SOA) also said in a statement that a fleet of the China Coast Guard (CCG) patrolled territorial waters around the Diaoyu Islands on Saturday. Japan’s Foreign Ministry said on Thursday that four Chinese coastguard vessels had entered the area near the islands on Wednesday and were still there, marking the longest sailing by Chinese ships in the disputed waters since the long-simmering dispute erupted again last year. A Japanese Foreign Ministry spokesman said later in the day that Tokyo had submitted a protest letter to China’s acting Ambassador Han Zhiqiang over the incident. Sovereignty over the territories has been a bone of contention between Asia’s largest economies for a long time. The islands are controlled by Japan now, but Beijing has also laid claim on them. The Islands are located near a crucial shipping lane and would give the owner exclusive oil, mineral and fishing rights in the surrounding waters. On September 11, 2012, Tokyo signed a deal to buy three of the islands from their private Japanese owner in line with plans to nationalize the archipelago. In late April, Japanese Prime Minister Shinzo Abe said Tokyo would “expel by force” any Chinese individuals landing on the islands, following an incident where eight Chinese vessels entered the disputed waters.