Japan has launched its largest military ship since the second world war, the 19,500-ton Izumo, at a ceremony in Yokohama, Kyodo News reported.

The 813-foot-long, 125-foot-wide destroyer will be deployed with the Maritime Self-Defense Force in March 2015.

The destroyer, built by IHI Marine United -- previously called Ishikawajima-Harima Heavy Industries -- will be helicopter-equipped and the first of two Izumo-class ships planned by Japan.

The Izumo's flight deck is nearly 820 feet long and can carry as many as 14 helicopters.

But the deck is not a ski-jump design and there is no catapult system that would enable conversion into an aircraft carrier.

A report by DefenseTalk in 2010 suggested that because of the large deck, the vessel could carry vertical take-off and landing aircraft, such as Lockheed Martin's F35B variant of the Strike Fighter.

The Izumo and its forthcoming sister ship, yet to be named, compliment Japan's two recently-built 13,950-ton Hyuga-class helicopter destroyers, also built by IHI Marine United.

The Hyuga, was commissioned in March 2009 and is stationed in Yokosuka, near Tokyo.

The second Hyuga-class ship, Ise, was inducted into service in March 2011 and is stationed at Kure.

The launch of the Izumo comes as Japan is increasingly concerned about protecting its territorial waters in face of challenges by Chinese coast guard and fishing vessels.

On Wednesday, Kyodo reported that four Chinese coast guard ships entered Japanese territorial waters near the disputed Senkaku Islands in the East China Sea.

Coast Guard officials said the incursion was the 56th incident since Japan purchased part of the uninhabited islet group, which China claims and calls Diaoyu, from a private Japanese businessman in September.

A Japanese coast guard vessel warned the Chinese ships to stay clear of the islands, the Kyodo report said.

Before leaving the area, one of the four vessels said in Japanese and Chinese the islands have been Chinese territory since ancient times.

China maintains the Senkaku Islands, which lie around 100 miles north of Japan's Ishigaki Island and 116 miles northeast of Taiwan, have been its territory since international treaties in the late 1800s.

China's official news agency Xinhua reported in January the National Administration of Surveying, Mapping and Geoinformation was to start surveying the Senkakus as part of a national survey project of Chinese islands in the area.

Concerns have been raised by Japan and other countries bordering the East China Sea over Chinese intentions in the region regarding disputed islands, especially since China's first aircraft carrier entered service in September last year.

The 55,000-ton carrier, formerly known as the Soviet ship Varyag, was renamed Liaoning during a commissioning ceremony, China's state-owned newspaper China Daily reported at the time.

China is among the small group of nations -- the United States, the United Kingdom, France, Russia, Spain, Italy, India, Brazil and Thailand -- operating aircraft carriers.

China bought the hull of the unfinished vessel in 1998, with no guns or engines, from a Ukrainian shipyard where it had been under construction.

The aircraft carrier was unfinished when the Soviet Union collapsed in 1991, leaving Ukraine with Soviet bases and equipment.

China insists the Liaoning is for scientific and training purposes only.