China has criticised Japan over its new defence plan, which includes getting its first aircraft carriers since World War II and buying dozens of fighter jets.

Japan said it had "strong concerns" about the expansion of China's military footprint on Tuesday, prompting China's Foreign Ministry spokeswoman Hua Chunying to accuse Japan of making "thoughtless remarks".

"What Japan is doing here is not conducive to improving and developing China-Japan relations, nor to the broader picture of regional peace and stability," she said.

"China expresses strong dissatisfaction and opposition to this and has already lodged stern representations with Japan."

AP

The new five-year defence plan calls for the upgrade of two existing helicopter carriers so that they can launch fighters, and is the latest in a series of steps under Prime Minister Shinzo Abe to boost Japan's military.

Abe's government argues the efforts are necessary given growing defence challenges in the region.

But the move is controversial, with critics arguing it shifts Tokyo further away from its commitment to strictly defensive capabilities under Japan's post-World War II pacifist constitution.

"We will secure both the quantity and quality of defence capability that is necessary... to meet the rapidly changing security environment," Chief Cabinet Secretary Yoshihide Suga told a regular press briefing on Tuesday.

"We believe this is within... what is allowed under the constitution."

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The five-year plan approved Tuesday assumes record defence spending of 27.47 trillion yen ($244 billion) through March 2024.

It calls for the defence ministry to upgrade two flat-top Izumo-class destroyers to enable them to launch fighters with short take-off and vertical landing abilities, like the F-35B stealth fighter.

In a separate plan also endorsed by the cabinet Tuesday, Japan said it would buy 42 F-35s over the next decade, with the F-35B variant widely considered the likeliest candidate.

It also plans over the same period to buy 105 F-35As, a variant of the advanced jet which performs conventional takeoffs and landings and cannot be used on the retrofitted destroyers.

Local media have said the purchases could total more than one trillion yen ($8.8 billion).

Worries about China

The new plans come after pledges from Japan to buy more US military equipment, under pressure from President Donald Trump, who has repeatedly complained about Washington's huge trade deficit with Tokyo and also urged Abe to expand the country's defensive capacity.

Abe has aggressively expanded Japan's alliance with the United States.

He has campaigned for years to amend Japan's pacifist constitution, arguing that it ties the hands of the country's Self-Defense Forces (SDF) even in protecting the country's allies from attack.

AP

Government officials were at pains to make clear the policy did not represent a shift away from the country's long-standing focus on defence.

"The Izumo-class destroyers will continue to serve as multi-function, multi-purpose destroyers. This mode of operation falls within the realm of an exclusively defence-oriented policy," Defence Minister Takeshi Iwaya told a regular briefing.

The remodelled ships and new fighter jets will "increase operational flexibility" for Japan's military as China boosts its naval footprint in southern waters that are home to several remote Japanese islands, a defence official said.

"We have a very, very small SDF footprint" in the area between Okinawa and Taiwan, he added.

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But he said it was a "misunderstanding" to believe that the upgrades would create "full-fledged aircraft carriers" capable of staging offensive action in distant regions.

And the new fighters would be stationed at existing ground facilities, not on the ships, he said.

"We are not creating carrier air wings or carrier air squadrons" like the US navy, he added.

"That's not going to happen."