Japan is set to spend some $8 billion to upgrade its air capability, possibly opting for a fleet of radar-evading F-35 combat jets manufactured by American firm Lockheed Martin, reports said.

According to Reuters, Tokyo's other options are Boeing's F-18 Super Hornet and the Eurofighter Typhoon, a product of a partnership by four European nations.

The move is largely seen as Japan's gradual departure from its pacifist policy adopted after the debacle of the Second World War, and as a creeping response to the military buildup in China.

Reuters said China has increased its defence spending by at least 12 percent this year, marking its intent to make its military presence felt in the region and highlighted by the introduction of its first aircraft carrier and in-house jet fighter - the stealthy J-20.

Purchasing new aircraft, especially the new F-35s, would at least ensure that Japan will not be left behind as regional powers start flexing their muscles, analysts said.

Apart from China, India, Indonesia and Australia have either been beefing up their military wares or forging alliances to shore up their positions as the region emerges as the world's next political and economic hotspot.

"The decision should be in line with what China has anticipated and come with little surprise," Narushige Michishita of Japan's National Graduate Institute for Policy Studies told Reuters.

Yet as a matter of policy, Michishita added that Chinese officials should issue perfunctory statements that decry the military build-up of possibly its strongest rival in the region.

For decades, Japan has relied on the United States for defence and kept its own military profile low while sending its troops abroad to serve as peacekeepers for the United Nations.

Its current military expansion will be facilitated, according to Lockheed Martin executives, once Japan does away with its strict regulation of local military suppliers.

Once that one stumbling block has been removed, Japanese contractors such as Mitsubishi Heavy Industries can look forward "to very strong case for participating in the F-35 program," Dave Scott of the F-35 international business development told Reuters.

The F-35 has been touted as Japan's primary choice, owing to the combat plane's superior stealth features and capabilities, defence analysts said.