TOKYO • Japan has opened the headquarters of a new unified command for the military's five regional armies and a new amphibious brigade tasked with defending its remote islands.

The new central command station is housed at a military base in Asaka, just north of Tokyo, the Wall Street Journal said on Wednesday.

The Ground Self-Defence Force (GSDF) last month launched the new Ground Central Command, which will provide unified command over regional armies and the new Amphibious Rapid Deployment Brigade, similar to the US Marine Corps.

The organisational shake-up is among the biggest in Japan's post-war military history and the biggest ever for the GSDF, the Journal said.

The new Ground Central Command will assume unified command over all ground troops across the country, under the orders of the Defence Minister.

There was no need to worry about civilian control of the military, Defence Minister Itsunori Onodera told reporters on Wednesday,in quotes carried by Reuters.

Unlike the air and maritime branches of the Self-Defence Forces (SDF), each with a unified command, the GSDF previously had no central headquarters to control its units across five regional armies.

Therefore, orders had to be issued to each regional army to mobilise its divisions and brigades.

The new command is also expected to facilitate communication with the US military in Japan. About 50,000 US troops are based in Japan under a security-treaty alliance.

Hours before the command station opened, Japan reported seeing Chinese coast guard ships sailing for the third successive day in waters near East China Sea islands controlled by Tokyo but claimed by Beijing, the Journal said.

China calls the uninhabited islands Diaoyu and Japan refers to them as the Senkakus.

"(China's) unilateral escalation is a matter of strong concern," Mr Onodera said in a speech to mark the opening of the combined army command.

The new Amphibious Rapid Deployment Brigade is the other highlight of the massive reorganisation.

The GSDF's first full-scale amphibious operations unit is launched with around 2,100 members mainly drawn from the Western Army's infantry regiment stationed at Camp Ainoura in Sasebo, Nagasaki Prefecture.

The creation of the new unified command is part of a broad review and upgrade of Japan's SDF, which many Japanese still associate more with disaster relief and peacekeeping than warfare.