Billed as Japan's biggest defence export deal since World War II, Australia will pay US$6 billion (Aus$10 billion) over the next 10 years to acquire the fleet of stealth frigates.

Australia is in the midst of a major military restructure, bolstering its navy with long-range firepower in an effort to deter China.

It is striving to expand its fleet of major warships from 11 to 26 over the next decade. 

"This is clearly the biggest defence-industry agreement that has ever been struck between Japan and Australia," Marles said, touting the deal. 

"This decision was made based on what was the best capability for Australia," he added.

"We do have a very close strategic alignment with Japan."

Mitsubishi Heavy Industries was awarded the tender over Germany's ThyssenKrupp Marine Systems.

Mogami-class warships are advanced stealth frigates equipped with a potent array of weapons. 

Marles said they would replace Australia's ageing fleet of Anzac-class vessels, with the first Mogami-class ship to be on the water by 2030. 

"The Mogami-class frigate is the best frigate for Australia," said Marles. 

"It is a next-generation vessel. It is stealthy. It has 32 vertical launch cells capable of launching long-range missiles."

The deal further cements a burgeoning security partnership between Australia and Japan. 

Japan is deepening cooperation with US allies in the Asia-Pacific region that, like Tokyo, are involved in territorial disputes with China.

Both Japan and Australia are members of the "Quad" group alongside India and the United States. 

For Japan, the frigate sale is further step in its efforts to forge security ties beyond its alliance with the US as it seeks to counter China's expanding military power in Asia.

"The benefits include enhanced joint operations and interoperability with both Australia and the United States. This is a major step forward in Japan’s defence cooperation efforts," Japan's Minister of Defence Gen Nakatani said at a briefing in Tokyo.

Japanese government spokesman Yoshimasa Hayashi said Tuesday the deal was "proof of trust in our nation's high-level technology and the importance of interoperability between Japan's self defence forces and the Australian military."

It was also a "big step toward elevating the national security cooperation with Australia, which is our special strategic partner", Hayashi told reporters in Tokyo.

Japan's pacifist constitution restricts it from exporting weapons -- but in 2024 Tokyo loosened arms export controls to enable it to boost sales abroad.

The order is Japan's biggest defence export deal since World War II, according to local media.

Designed to hunt submarines, strike surface ships and provide air defences, the highly automated warships can be operated by just 90 sailors, less than half the crew needed for current vessels.

Australia plans to deploy the new ships to defend critical maritime trade routes and its northern approaches in the Indian and Pacific Oceans, where China has been increasing its presence and activity.

Defence industry minister Pat Conroy said the Mogami-class frigates were capable of launching long-range Tomahawk cruise missiles. 

"The acquisition of these stealth frigates will make our navy a bigger navy, and a more lethal navy," he said. 

The first three Mogami-class frigates will be built overseas, Conroy said, with shipbuilding yards in Western Australia expected to produce the rest.

Australia announced a deal to acquire US-designed nuclear-powered submarines in 2021, scrapping a years-long plan to develop non-nuclear subs from France. 

Under the tripartite AUKUS pact with the United States and the United Kingdom, the Australian navy plans to acquire at least three Virginia-class submarines within 15 years. 

The AUKUS submarine programme alone could cost the country up to US$235 billion over the next 30 years, according to Australian government forecasts, a price tag that has stoked criticism.

Major defence projects in Australia have long suffered from cost overruns, government U-turns, policy changes and project plans that make more sense for local job creation than defence.

Australia plans to gradually increase its defence spending to 2.4 percent of gross domestic product -- above the 2 percent target set by its NATO allies, but well short of US demands for 3.5 percent.