Nobuo Kishi warned the gap between Japan and China's military was "growing by the year," in an interview with the Nikkei newspaper.

"We must increase our defence capabilities at a radically different pace than in the past," he said, citing China's military spending as well as new areas of warfare including space, cyber and electromagnetics.

Japan's defence spending has tended to hover at around one percent of GDP, but Kishi said that spending would be guided by needs rather than caps.

"The security environment surrounding Japan is changing rapidly with heightened uncertainty," the Nikkei quoted him as saying.

"We will properly allocate the funding we need to protect our nation."

Japan's post-war constitution limits the scope of its military to defensive power, and efforts to boost capacity have sometimes been controversial domestically.

Kishi's comments come with Japan increasingly concerned about the regional security environment and particularly China's growing assertiveness.

The military balance between Japan and China has "leaned heavily toward China in recent years, and the gap has been growing by the year," he told the paper.

Kishi also said Japan considers issues related to Taiwan "as our own problem", as China increases pressure on the self-ruled island territory, which Beijing sees as a rebel province.

Japan has been more vocal in recent months about Chinese moves in regional waters, and particularly the presence of coastguard ships around disputed islands in the East China Sea.

In talks last month, Japanese Prime Minister Yoshihide Suga and US President Joe Biden discussed concerns over Beijing's maritime moves, as well as clampdowns in Hong Kong and Xinjiang, and growing tension over Taiwan.

The United States has long pressed Japan and its allies to increase their military capacity.