China’s Nuclear Buildup Raises New Questions Ahead of Xi Visit

China is rapidly expanding its nuclear arsenal, testing increasingly sophisticated missile delivery systems, and facing accusations that it secretly detonated a nuclear weapon underground. At the same time, Beijing is imprisoning an American scientist whose specialty is detecting precisely those kinds of hidden nuclear explosions.

None of those facts alone proves that China is concealing a broader nuclear testing program. Taken together, however, they raise troubling questions about what Beijing is preparing for – and what it may be trying to hide.

Questions about China’s nuclear ambitions have become even more urgent following Secretary of State Marco Rubio’s August 20 designation of American scholar Min Zin as “wrongfully detained” by China. Min Zin is now the second American in Chinese custody to receive that designation, joining seismologist Youlin Chen, who has reportedly been subject to intense questioning and even torture over his research into nuclear test detection.

These developments come just weeks before President Donald Trump is expected to welcome Chinese leader Xi Jinping to the White House, where Beijing’s military buildup and its detention of American citizens should be near the top of the agenda.

Min Zin, a U.S. citizen, was detained at an airport in Yunnan on June 3 after traveling to China for an academic conference.

Youlin Chen, a Chinese-born American seismologist from Boston, has been imprisoned since November 2024 and charged with espionage. Chen’s wife says Chinese authorities have interrogated him more than 100 times about his research, including work on the seismic signatures of North Korean nuclear tests.

That detail is particularly noteworthy as evidence continues to accumulate that Beijing is rapidly expanding its nuclear arsenal while revealing little about its intentions.

The Stockholm International Peace Research Institute (SIPRI) estimates that China now possesses roughly 620 nuclear warheads, about twice as many as it had just five years ago. SIPRI says China is expanding its arsenal faster than any other country and has loaded hundreds of missiles into three large new missile silo fields.

As a result, China could have as many intercontinental ballistic missiles as the United States or Russia by 2030. The Pentagon has similarly projected that China could field more than 1,000 nuclear warheads by the end of the decade.

Beijing provided another reminder of that growing capability in July, when a Chinese nuclear-powered submarine launched a nuclear-capable long-range ballistic missile carrying a dummy warhead into the Pacific. China called the exercise routine and said it was not directed at any country.

But the test alarmed governments throughout the region. Australia called it “destabilising,” while New Zealand Foreign Minister Winston Peters described it as part of a “recurring pattern” and warned against normalizing Chinese missile testing in the South Pacific.

Quán Chāngpǔ, a retired People’s Liberation Army officer and Chinese dissident interviewed for this article, said the launch reflects a more aggressive mood inside portions of China’s military. Senior PLA officers, he said, “understand consequences,” while some younger officers are “too eager.”

The July launch demonstrated Beijing’s improving ability to deliver nuclear weapons from submarines, an important component of a force designed to survive an attack and retaliate.

More troubling are U.S. allegations that China may already have resumed nuclear testing in secret. In February, Assistant Secretary of State for Arms Control and Nonproliferation Christopher Yeaw publicly accused China of conducting a concealed low-yield underground nuclear test at its Lop Nur test site on June 22, 2020.

Yeaw said seismic data showed an explosion inconsistent with either an earthquake or mining activity. He also accused China of using “decoupling,” a technique in which an explosion occurs inside a large underground chamber to reduce the seismic shock waves that monitoring stations can detect.

This development makes the Chen case all the more significant. Chen has published U.S.-funded research on detecting underground nuclear tests. A 2020 paper from Chen examined North Korea’s six known nuclear explosions and methods for distinguishing their seismic signatures from earthquakes.

Chen’s wife says his Chinese interrogators repeatedly focused on precisely this area of research. She also says Chen was initially forced to sit all day on a hard stool, was denied access to his lawyer for more than a year, and has lost 30 to 40 pounds in detention.

Eric Lebson of Global Reach, a hostage advocacy organization assisting Chen’s family, has said he believes Chinese officials may want Chen’s expertise to improve their ability to conceal underground nuclear tests through decoupling. Other nuclear experts consulted by the organization expressed similar concerns.

There is no public evidence proving that Chen was detained for that reason. But the overlap is difficult to ignore. China is conducting the world’s fastest nuclear buildup; U.S. officials accuse China of secretly testing a nuclear weapon using methods intended to avoid seismic detection; and the Chinese Communist Party is unjustly detaining an American scientist with expertise in detecting exactly those kinds of explosions.

Chinese authorities insist Chen is a spy. His family says his research was transparent and lawful.

A Chinese dissident and former CCP official interviewed for this article, Dr. Wu Shunli, rejected accusations portraying Chen’s scientific work as espionage, calling them a “pathetic lampoon and a vile attack on this man’s moral character.”

The broader issue is no longer limited to Chen. With Min Zin’s designation last week, the United States now officially considers two Americans in Chinese custody wrongfully detained.

Kieran Ramsey of Global Reach has described Chen’s case as an example of Beijing’s willingness to use “hostage diplomacy” in its competition with Washington.

President Trump is scheduled to welcome Xi to the White House on September 24. The meeting gives him an opportunity to demand answers on both issues — China’s increasingly opaque nuclear buildup and the Americans Beijing continues to hold.

Trump also has leverage. Under an executive order he signed last year, the Secretary of State can designate countries that engage in wrongful detention as State Sponsors of Wrongful Detention, opening the door to sanctions, visa restrictions, travel limits, and export controls.

China may insist that each of these developments has an innocent explanation. Perhaps the missile tests are routine, the 2020 seismic signals were something other than a nuclear explosion, and Chen’s detention has nothing to do with his expertise in detecting clandestine tests – although for all the reasons presented here, those claims are highly doubtful.

But governments should be judged by what they actually do, not just by what they publicly say. Beijing is building nuclear weapons at extraordinary speed, resisting transparency, testing increasingly capable delivery systems, and imprisoning an American scientist whose work could help expose what happens beneath the ground at China’s nuclear test sites.

President Trump should demand answers for all of this in his meeting with Xi. In nuclear affairs, uncertainty is dangerous enough. Deliberately creating it is more dangerous still.