Japan emphasised China as a threat in escalating regional tensions as Prime Minister Shinzo Abe's government tries to convince the public of the need to give the nation's military a greater role.

This year's annual defence report has now been approved by the cabinet after it was delayed for more than a week as Mr Abe's ruling party demanded mention of additional examples of China's "one-sided" maritime activities, such as undersea gas and oil development in the East China Sea.

Mr Abe's ruling coalition has been pushing to pass highly contentious legislation allowing Japan's Self-Defence Force to fight for foreign militaries even when it is not under attack, while expanding its role in international peacekeeping.

China by far topped Japan's list of security concerns, taking up one-third of a chapter on global security trends covering eight countries and regions.

The 429-page white paper underscored that Japan's security risk had worsened overall and cited continuing missile and nuclear threats from North Korea and terrorist threats from the Islamic State group as examples.

The report raised concerns over China's recent reclamation work in the South China Sea, saying it had escalated regional tensions. It also added a new section that also refers to maritime activities elsewhere.

China has been building artificial islands in the vast, resource-rich area, alarming neighbouring nations.

"China, particularly over conflicting maritime issues, continues to act in an assertive manner, including coercive attempts to change the status quo, and is poised to fulfil its unilateral demands high-handedly without compromise," the report said.

"Japan is strongly concerned about China's actions, which we need to keep watching closely."