Japan on Tuesday chose the as-yet unproven F-35 stealth jet for its next-generation mainstay fighter, as North Korea provided a timely reminder of the region's potential for instability.

In a deal worth around $4.7 billion, Japan plumped for the jet to replace its ageing fleet of F-4 fighters, despite a series of technical setbacks and fears that the US-built F-35 might be badly delayed.

"The government shall acquire 42 units of the F-35A after fiscal 2012 in order to replenish and to modernise the current fleet of fighters held by the Air Self-Defense Force," the cabinet said in a statement.

Lockheed Martin's F-35 beat off competition from two other jets -- the Boeing-made F/A-18 Super Hornet and the Eurofighter Typhoon.

The formal decision, which had long been expected, came the day after news of the death of Kim Jong-Il sent jitters through the region amid fears a power transition could destabilise North Korea's hardline regime.

Japan was originally expected to announce its pick last week. The selection comes as China's massive military machine continues to grow and becomes increasingly assertive.

Tokyo and Beijing have butted diplomatic heads on a number of occasions, notably in a protracted -- and at times ugly -- spat over disputed islands in the East China Sea, known in Japan as Senkaku and in China as Diaoyu.

Both countries claim sovereignty over the Japanese-administered islands, which are strategically important, but uninhabited, outcrops.

Beijing, whose military spending has grown by double digits every year for much of the past decade, is seen as using its economic and military might to press its territorial claims ever more aggressively.

In January it unveiled its own stealth fighter jet.

In the six months to September, Japanese jets were scrambled 83 times to respond to possible airspace violations by Chinese aircraft, Jiji press reported, a more than three-fold increase on the same period last year.

Defence Minister Yasuo Ichikawa said the F-35 fitted the bill as a modern fighter plane, suited to Japan's needs.

"It was about its capability. It is a fighter with capacity to respond to the changing security environment."

With a price tag of around $113 million per jet, the F-35 is the most expensive weapons programme in Pentagon history and has been plagued by cost overruns and technical delays.

Last week a leaked memo revealed an array of problems exposed by flight tests, including with the landing gear and issues over airframe fatigue and vibration.

The report, dubbed a "Quick Look Review" at the F-35 programme, said the technical challenges generated "a lack of confidence in the design stability" of the aircraft, which has already started production.

As a result, the review calls for "serious reconsideration of procurement and production planning", it said.

A spokesman for the fighter programme confirmed that managers were looking at scaling back the pace of production to allow time to fix the technical problems that had emerged.

However, Ichikawa said he was confident the hardware would arrive in Japan by 2016.

"We have received assurances that the delivery will be made on time," he said.

Japan initially aimed to acquire the F-22 stealth fighter to renew its fleet, but US law prohibits exports of the jet and the United States plans to halt production of the model.

Japan, which places its security alliance with the United States at the cornerstone of its foreign policy, has long depended on US manufacturers for its military hardware.

The United States welcomed the announcement.

"We are pleased with the decision of the government of Japan to purchase a US candidate platform," the US embassy said in a statement.

"This decision reflects the vitality of our alliance and will greatly enhance our bilateral cooperation and interoperability," it said, adding it would create about 10,000 news jobs in the United States alone.