With one missile fired over the Pacific Ocean from a submarine lurking off China’s coast, the country’s leader, Xi Jinping, has proclaimed his determination to build a full suite of nuclear weapons, including sea-based missiles that have long been Beijing’s weak spot.

The missile test on Monday came after China’s military has been battered for years by mass removals of commanders accused of corruption and disloyalty. But Chinese media declared that the test showed the country remained on track to create a full nuclear triad; that is, a range of land-, air- and sea-based weapons that could give Beijing a stronger hand in a regional crisis or war with the United States.

Chinese officials have been muted about the test and its implications. Not the Global Times, a Chinese newspaper controlled by the Communist Party.

“Our national nuclear triad had another upgrade,” the paper said in an article on Tuesday.

“The Liberation Army’s sea-based nuclear force is capable of carrying out stable, reliable strategic counterstrikes from anywhere in the vast open seas of the Pacific Ocean,” it said, citing a Chinese expert.

That claim is hyperbole: China is still some way from operating nuclear-armed submarines undetected and wherever it likes. Even so, the test indicated that China is expanding its undersea nuclear ambitions, and shedding its reluctance to test missiles in international skies and oceans, despite the scrutiny and alarm such exercises set off, several experts said.

“Most basically, China needed to technically validate its newest submarine-launched ballistic missile capability. But there was a broader message to the world — China now has a fully operational nuclear triad,” said Evan S. Medeiros, a professor at Georgetown University and a former China director in the National Security Council under President Obama. “China is probing the boundaries of U.S. defense strategy.”

For decades, China kept a relatively modest nuclear arsenal — much smaller than those of the United States and Russia — and has usually tested its nuclear-capable missiles within its own land borders. This was only the third time that China has conducted a long-range test of a missile across the Pacific. The first was in 1980; the most recent in 2024.

But as China’s nuclear weapons multiply and diversify, and as Beijing grows more confident in its global status, more tests may come. This time, China’s leaders also may have been happy to send a warning to the region and to Washington: that Beijing is capable of projecting power in new and intimidating ways, some experts said.

The location of the submarine that launched the missile was not immediately clear. Chinese maritime authorities had released notices on Monday warning about possible hazards in the seas off China’s northern and southeastern coasts.

Officials from two governments in the region said on the condition of anonymity that initial assessments indicated the missile was launched from the South China Sea, off southern China.

But other experts said the missile may have been launched near the Bohai Bay on the northeastern Chinese coast and arced southeast for more than 4,300 miles, landing in the sea off the Solomon Islands. (The Japanese government said the missile did not pass through Japan’s airspace or exclusive economic zone.)

“China is telling the world that it has a very large stick with which it will be able to dominate the Pacific,” said Justin Bassi, a former national security adviser in the Australian government who is now the executive director of the Australian Strategic Policy Institute in Canberra.

He noted China’s recent ire at Japan and Australia, including over Canberra’s recent security agreement with Fiji in the Pacific.

“China does not want the Australian and Japanese counter-influence, interference and coercion approach to be taken up by others in the region,” Mr. Bassi said.

Racing to Catch Up

Still, such tests take months of preparation, and the latest one was above all driven by the Chinese government’s desire to narrow the United States’ lead in sea-based nuclear forces, experts said. Even as China has rapidly expanded its land-based long-range missiles, its nuclear capabilities at sea have lagged.

Nuclear submarines rely on quiet stealth for their menacing power; their goal is to evade detection, forcing adversaries to fear an unexpected strike from the depths. But for decades, Chinese nuclear submarines were notoriously noisy, sending out rumbles and squeaks that other navies could detect with sonar.

China is still some distance from matching the standards set by the United States and Russia in submarine stealth and submarine-based nuclear missiles.

But the country has been investing heavily to close the gap, said Bruce Jones, a scholar at the Brookings Institution and the author of a forthcoming book, Sub War, about global undersea rivalry.

“China is racing to catch up in quality, and poised to surge ahead in numbers,” he said. “It’s likely we’ll see more tests.”

China has about 14 nuclear-powered submarines, including six that are nuclear-capable, Rear Adm. Mike Brookes, the commander of the U.S. Office of Naval Intelligence, told a congressional commission in March. The United States has around 70 nuclear submarines. But China has ramped up its production rates.

It is unclear what submarine China fired the missile from, and what kind of missile it was. Beijing rarely releases such details.

Some experts believe that the submarine was the Type 094 — China’s most advanced model in wide use — and that the missile was probably a JL-3, an intercontinental ballistic missile that China displayed at a big military parade last year. The Pentagon has said that the missiles have been installed on Type 094 submarines.

China is building a new generation of submarines that will be stealthier than the Type 094, possibly approaching capabilities achieved by an advanced Russian model, Andrew Erickson, a professor at the U.S. Naval War College, wrote in a study published this week.

“China’s quieting approach remains imperfect but is determined, comprehensive and improving,” Professor Erickson wrote, referring to the technology used to make submarines hard to detect. He emphasized his conclusions were his own, and did not represent the Naval War College or the U.S. Navy.

More Tests Are Likely

China is likely to conduct more testing of its submarine-based nuclear missiles by firing them into the Pacific Ocean, despite the criticism Monday’s test drew from Japan, the Philippines, Taiwan, Australia and the United States, said several experts.

“China conducts a lot of missile tests, but the overwhelming majority of them go toward the interior,” William Alberque, the former director of an arms control and disarmament center under NATO, wrote by email.

The United States conducts five to 10 tests of its Minuteman and Trident missiles over the Pacific every year, according to Mr. Alberque. Russia’s tests are conducted mostly from the Barents Sea, flying toward east Russia.

China has previously conducted secret tests of submarine missiles in the Bohai Bay area, Lyle Morris, a senior fellow at the Asia Society’s Center for China Analysis, wrote in an assessment of Monday’s test. Long-range tests allow missiles to be tested in conditions that resemble the heat and turbulence of real wartime trajectories.

The likely launch location of China’s latest test fits with its emerging “bastion” strategy for its submarine-launched nuclear missiles, wrote Mr. Alberque, now a senior analyst at Pacific Forum. Under that approach, China’s submarines lurk in seas close to its coast, protected by cordons of defense against detection and attack. From there, China’s JL-3 submarine-launched nuclear missiles could strike large parts of the U.S. west coast.

In those bastions, Mr. Alberque wrote, “they’re reasonably sure they can’t be ‘got’ by the U.S. if they had to fire off the big beasts.”

Javier C. Hernández contributed reporting from Tokyo.