Australia has unveiled plans to buy up to five U.S. nuclear-powered submarines, then build a new model with U.S. and British technology under an ambitious plan to bulk up Western muscle across the Asia-Pacific in the face of a rising China.

The announcement came on Monday at an event at a San Diego, California, naval base where U.S. President Joe Biden hosted Australian Prime Minister Anthony Albanese and British Prime Minister Rishi Sunak.

With a U.S. Virginia-class nuclear submarine moored behind the trio’s podium, Mr. Biden said the U.S. had “safeguarded stability in the Indo-Pacific for decades” and that the submarine alliance would bolster “the prospect of peace for decades to come.”

As Mr. Biden stressed, Australia, which joined a newly formed alliance known as AUKUS with Washington and London 18 months ago, will not be getting nuclear weapons.

However, acquiring stealthy submarines powered by nuclear reactors puts Australia in an elite club and at the forefront of U.S.-led efforts to push back against Chinese military expansion.

Mr. Albanese said the deal represents the biggest single investment in Australia’s defence capability “in all of our history.”

The submarines are expected to be equipped with cruise missiles that can strike foes from long distances, offering a potent deterrent to would-be attackers.

Mr. Albanese predicted that the wider economic impact at home would be akin to the introduction of the automobile industry in the country after World War II.

Meanwhile, the UN nuclear watchdog on Tuesday said it has to ensure that “no proliferation risks” will come from the deal.

“Ultimately, the agency must ensure that no proliferation risks will emanate from this project,” International Atomic Energy Agency chief Rafael Grossi said. “The legal obligations of the parties and the non-proliferation aspects are paramount,” Mr. Grossi added.

The U.K. and the U.S., both nuclear-weapons states, have to report to the IAEA “international transfers of nuclear material” to non-nuclear-weapon states such as Australia, the press release said.

Australia, for its part, will have to make “an arrangement” with the UN watchdog to be able to use nuclear material “such as nuclear propulsion for submarines”, Mr. Grossi stressed.

The Australian government estimates the multi-decade project will cost almost $40 billion in the first 10 years, and create an estimated 20,000 jobs.

Three conventionally armed, nuclear-powered Virginia class vessels will be sold “over the course of the 2030s,” with the “possibility of going up to five if that is needed,” Mr. Biden’s national security advisor, Jake Sullivan, said.

Britain and Australia will then embark on building a new model, also nuclear-powered and carrying conventional weapons, dubbed the SSN-AUKUS. This will be a British design, with U.S. technology, and “significant investments in all three industrial bases,” Mr. Sullivan said.