Tokyo will launch its first aircraft carriers since the end of World War II to accommodate a growing number of stealth fighters, long-range missiles and other equipment adding to the Japan Self-Defence Forces (JSDF).

Key points: Two helicopter carriers will be modified to become aircraft carriers

Two helicopter carriers will be modified to become aircraft carriers The announcement forms part of a 10-year defence program outlined by Tokyo

The announcement forms part of a 10-year defence program outlined by Tokyo Pacifism is enshrined in Japan's constitution

The guidelines approved at a meeting of Prime Minister Shinzo Abe's Cabinet call for refitting the Izumo helicopter carrier into a ship that can deploy expensive, US-made F-35B stealth fighters capable of short take-offs and vertical landings.

The work would be done over five years and the ship would carry 10 stealth fighters, while the refitting of a second helicopter carrier into a second aircraft carrier would follow.

Japan launched the world's first purpose-built aircraft carrier in 1922. ( Yokosuka Naval Arsenal )

The Prime Minister's guidelines would replace the current defence plan halfway through its intended lifespan and underscore Mr Abe's push to expand Japan's military role and capability to make it, as he puts it, "a normal country."

Defence officials say Japan needs better deterrence and increased missile defence and fighter capability as North Korea's missile and nuclear threats remains unchanged in the absence of concrete steps to dismantle them, and China's maritime activity has grown increasingly assertive.

The new guidelines say Japan needs to be well-prepared and to show it can withstand threats, noting the archipelago is prone to natural disasters and its coastline is dotted with vulnerable nuclear power plants.

Japan has relatively little land on which to build runways long enough for conventional F-35s, and an aircraft carrier would be particularly useful in the western Pacific, where Japan tries to defend remote islands, including those disputed with China, and to play a greater role as part of the US-Japan alliance.

Japan to add 147 F-35 stealth fighters to defence force

The Royal Australian Air Force has also ordered F-35s, dubbed the "most lethal acquisition" in history. ( Kyodo News via AP: Takuto Kaneko )

Japan plans to buy 147 F-35s, including 42 F-35Bs, over the next decade.

These stem from the same class of fighters procured by the Royal Australian Air Force (RAAF), labelled the "most lethal acquisition in the Air Force's history".

The new planes will include 18 short take-off and vertical landing (STOVL) B variants of the F-35 that planners want to deploy on Japanese islands along the edge of the East China Sea.

The islands are part of a chain stretching past Taiwan and down to the Philippines that has marked the limit of Chinese military dominance east of the disputed South China Sea.

"Japan's decision to acquire more F-35s is a testament to the aircraft's transformational capability and its increasing role in promoting regional stability and enhancing the US-Japan security alliance," Lockheed Martin said in a statement.

The navy's two large helicopter carriers, the Izumo and Kaga, will be modified for F-35B operations, the paper said.

The 248-metre-long Izumo-class ships are as big as any of Japan's aircraft carriers in World War II.

They will need reinforced decks to withstand the heat blast from F-35 engines and could be fitted with ramps to aid short take-offs, two defence ministry officials said.

Japan has the world's eighth-strongest military

Article nine of Japan's constitution explicitly rules out the use of force, but speculation is mounting Tokyo may change this. ( US Army: Markus Castaneda )

Japan plans to spend 25.5 trillion yen ($315 billion) on military equipment over the next five years, 6.4 per cent more than the previous five-year plan.

Cost-cutting will free up another $24.7 billion for purchases, the procurement paper said.

Japan only spends about 1 per cent of its gross domestic product (GDP) on defence, but the size of its economy means it already has one of the world's largest militaries.

In 2018, the Global Firepower index rated Japan as having the eighth-strongest military in the world.

Wary of North Korean promises to abandon ballistic missile development, Japan's military is buying longer-range Raytheon SM-3 interceptor missiles to strike enemy warheads in space.

"The budget is increasing and there has been an acceleration to deploy capability as soon as possible," Robert Morrissey, head of Raytheon Co's unit in Japan, said.

The defence papers assessed non-traditional military threats as well.

A new joint-forces cyber unit will bolster Japan's defences against cyber attacks. More electronic warfare capabilities are planned.

Japan's air force will also get its first space unit to help keep tabs on potential adversaries high above the Earth's atmosphere.

Wartime Imperial legacy has China spooked

Japan's Imperial Forces waged terror on its neighbours with Kamikaze pilots during World War Two. ( Shizuo Fukui )

The step is a major shift in Japan's post-war naval defence, which has lacked aircraft carriers in part out of concerns that they may remind Japan's Asian neighbours of aggression by Japan's Imperial Navy.

Critics say possession of an aircraft carrier would give Japan a strike capability in violation of Article Nine of its constitution which explicitly outlaws the use of force to settle disputes.

Japan, under the new defence guidelines, also plans to possess cruise missiles designed to hit enemy targets, which opponents say could violate its pacifist principles.

China urged Japan to stick to a defence-only policy and peaceful development.

"Due to historical reasons, neighbouring countries in Asia and the international community have long been highly concerned about Japan's moves in military and security fields," Chinese Foreign Ministry spokeswoman Hua Chunying told reporters.

Japan was making "groundless and irresponsible accusations against China's normal defence construction and military activities" to play up the China threat, she said.

Japanese officials brushed off the criticism, saying the Izumo will be a multifunctional warship used as an aircraft carrier only when necessary for national defence.

Chief Cabinet secretary Yoshihide Suga said the vessel was mainly for fighter pilots in case of an emergency at sea and that it "falls within the minimum necessity allowed under the constitution."

ABC/Wires