Japan bolstered its military surveillance capabilities in the southern island region of Okinawa over the weekend, reports said, as territorial tensions with China simmer.

The nation's armed forces, called the Self-Defence Forces, launched a squadron of four E-2C early warning planes at its air base in Naha on the main Okinawan island Sunday, the Jiji and Kyodo news agencies reported.

This is the first time such planes have been based on the island. At the inauguration ceremony in Naha, Defence Minister Itsunori Onodera said Japan faced a "dangerous situation" as China's continual attempts to "change the status quo by force and threaten the rule of law could trigger emergencies," Kyodo News reported.

"The squadron was newly established to firmly defend our country's territorial land, sea and air," he told reporters afterwards, according to Jiji Press.

Japan's air force possesses 13 E-2C airborne early warning planes at the Misawa base in northern Japan. Four of these have been transferred to the Naha base.

The number of personnel there will be doubled to about 130 by March 2015.

Japan scrambled fighter jets against approaching Chinese aircraft 415 times in the year to March 2014, up from 306 times in the preceding year, Jiji said citing defence ministry statistics.

On Saturday, a ceremony was held to start building a radar surveillance unit on Yonaguni, Japan's westernmost island, despite protests from islanders fearing the unit will trigger attacks, the reports said.

Yonaguni lies around 150 kilometres (100 miles) southwest of the Tokyo-controlled Senkaku islands which China also claims and calls the Diaoyus.

Chinese ships and planes have approached the disputed island group, repeatedly moving into its territorial waters and airspace, after Tokyo nationalised some of the Senkakus in September 2012, to confront Japanese patrols.

Radar equipment will be installed at the ground force unit on Yonaguni to monitor ships and aircraft in the East China Sea, the reports said.

About 150 personnel will be deployed at the radar unit by the end of March 2016.

"It's very important to take a solid surveillance posture on remote islands," Defence Minister Onodera said after attending the ground breaking ceremony on Saturday, Kyodo reported.

The unit will "fill a void of Self-Defence Forces presence" in Japan's remote southwestern islands, he added.

Both the main Okinawa island and Yonaguni are part of the island region of Okinawa.

The surveillance boost comes at a time when Japan's Prime Minister Shinzo Abe is pushing to reconfigure Japan's role in the world, specifically that of its armed forces.

He wants to re-interpret a law to allow Japanese troops to take up arms to defend an ally under attack in so-called collective self-defence.

Beijing has sought to paint Abe's moves as a dangerous slide back towards its militarism of the last century.

On Saturday some 70 Yonaguni islanders opposed to the new surveillance unit scuffled with officials connected to the defence ministry, Kyodo said.

The islanders were concerned Yonaguni could become a target in any future conflict between Japan and China.