The Diaoyu Islands are a group of uninhabited islands located roughly due east of mainland China, northeast of Taiwan, west of Okinawa Island, and north of the southwestern end of the Ryukyu Islands. They are currently controlled by Japan, which calls them Senkaku Islands. Both China and Taiwan claim sovereignty over the islands.
Diaoyus dispute has parallels with World War I, says scholar
Military scholar sees parallels between Europe on the brink of Great War and the standoff between China and Japan over disputed islands
Julian Ryall in Tokyo
Tensions between Japan and China over the sovereignty of the Senkaku Islands, which Beijing claims as the Diaoyu isles, have eased in recent months, but there is still an underlying drive to enhance naval capabilities on both sides, according to a leading military analyst.
The ongoing tensions were underscored on Thursday when three Chinese government ships plied waters around the islands, the Japanese coastguard said.
The maritime surveillance vessels entered the 12-nautical-mile zone regarded as the territorial waters of Uotsurijima, one of the islands, in the East China Sea shortly before 8.30am, the coastguard said. The three vessels left the zone after about three hours.
"International escalation is the key element here and there is always the possibility of unintended consequences, as in August 1914," said Dr Alessio Patalano, of the department of war studies at King's College, London.
"In the Senkakus, there is the chance of the Japan Coast Guard and a Chinese maritime surveillance vessel clashing, or perhaps a Chinese turboprop aircraft downed in an accident," he said. "That could force the governments into the position of an escalation to war. But I think this is looking a lot less likely than it did a few months back.
"Last year, there were domestically generated problems because of political transitions in both countries," he pointed out. "Both countries had political capital invested in the situation and neither side could give in. Now, the transition has been completed in both Japan and China."
A key point of concern is that both nations are committed to aircraft carrier programmes, even if Tokyo continues to refer to its platform as a "helicopter destroyer", Patalano said. "Chinese generals often speak of the importance for China to have at least one [carrier]," he said.
Defence reviews in Japan, in particular the 2010 review, led to an increase in the pace of the structural transformation initiated in the mid-1990s.
It also led to a reorganisation of the Japanese fleet, with the basic tactical formation shifting from an anti-submarine-warfare flotilla to an escort division with a helicopter destroyer.
Despite much debate over the future of the aircraft carrier as an effective tool of power protection, Patalano says he believes it will continue to play an important role for the foreseeable future.
"Yes, China is developing the 'carrier killer' ballistic missile, and while that is an important new threat that makes carriers more vulnerable, the jury is still out," he said.
"But the truth is that the aircraft carrier has always been a very vulnerable asset; it is a large target and even experts in anti-submarine warfare will tell you that theirs is a very inexact science.
"The existence of new countermeasures to carriers should not be seen as a reason to render carriers obsolete. "They have always exercised power and they still perform a lot of functions; 100,000 tonnes of steel and a lot of firepower can achieve a lot of things."
Additional reporting by Agence France-Presse