As major powers renew their focus on nuclear testing, the world may be entering a new nuclear era.
Revelations that Beijing has conducted secret nuclear tests should trigger greater focus on China’s expanding nuclear arsenal. China’s nuclear expansion and modernisation could lead to an accelerated and unbridled nuclear arms race, particularly since Chinese President Xi Jinping refuses to participate in meaningful dialogue and abide by agreements on such issues. This would have implications that go beyond the US-China competition: it would affect global stability; undermine international non-proliferation norms and efforts; and harm the prospects of future arms control agreements.
On 6 February, US Under Secretary of State for Arms Control and International Security Thomas DiNanno revealed that the US was aware that China had been conducting nuclear tests. One such test was conducted in June 2020, based on US assessments.
In a statement at the Conference on Disarmament, the United Nations’ multilateral platform for nuclear arms control in Geneva, DiNanno said:
The PLA sought to conceal testing by obfuscating the nuclear explosions because it recognised these tests violate test ban commitments. China has used decoupling—a method to decrease the effectiveness of seismic monitoring—to hide their activities from the world.
Typically, the Comprehensive Test Ban Treaty (CTBT) Office would be able to detect and record such tests. However, China’s efforts to hide its activities likely prevented detection by the office’s monitoring systems.
On 17 February, the US revealed further details. Assistant Secretary of State Christopher Yeaw provided details about seismic data from a monitoring station in Kazakhstan. He said the data was incompatible with anything other than a nuclear test, meaning it couldn’t simply be attributed to mining or an earthquake.
China has carefully responded to the US’s statements, saying the US has ‘no factual evidence.’
Jeffrey Lewis, a nuclear weapons and arms control expert, stated in a thread on X that ‘China, like the United States, has declared a moratorium on nuclear testing. The CTBT, though, bans “nuclear explosions”, not testing, but it does not define a nuclear explosion. The debate concerns whether China is abiding by our definition.’
There is some question about whether the CTBT really prohibits such tests. The treaty never entered into force, in part because it was never ratified by the US or China, which could lead some to suggest that China cannot have violated its commitments. But regardless of technicalities around treaties and definitions of nuclear explosions and tests, if sufficient evidence points to China’s resumption of nuclear testing, it is likely to push other countries to do the same.
Alongside its quantitative nuclear expansion, China has also been engaging in more vigorous missile testing activities. According to the Pentagon’s latest report on Chinese military power, China is pursuing nuclear weapons with yields of less than 10 kilotons for use on the DF-26 intermediate range ballistic missile or the H-6N bomber’s air-launched ballistic missiles. These low-yield weapons are considered a good fit for limited nuclear use.
This was not the first report on possible Chinese nuclear testing. In April 2020, The Wall Street Journal reported that ‘China might be secretly conducting nuclear tests with very low explosive power.’ US concerns in 2020 arose due to ‘the tempo of activity at China’s Lop Nur test site, extensive excavations at the site, and Beijing’s purported use of special chambers to contain explosions.’ In a 2025 research essay, Renny Babiarz and Jason Wang detailed a ‘dramatic expansion’ of the site between 2020 and 2024, indicating that China had been preparing ‘to conduct underground nuclear tests in support of new nuclear-weapons designs.’
In his statement, DiNanno also highlighted discrepancies between the US and Russia in adherence to New START, the arms treaty formerly in place between the two countries. He noted that ‘almost all of the US deployed nuclear forces were subject to New START while only a fraction of Russia’s much larger stockpile was,’ adding that ‘zero Chinese nuclear weapons were covered by New START.’
He said, ‘China’s entire nuclear arsenal has no limxits, no transparency, no declarations, and no controls.’ The US, he argued, ‘can now finally take steps … to strengthen deterrence … We will complete our ongoing nuclear modernisation programs that were initiated while New START entered into force.’ This suggests that the US may very well be preparing to respond in kind. President Donald Trump had already asked for the US to resume nuclear testing on ‘an equal basis.’
While China is expanding its nuclear arsenal at a dramatic pace, Russia and the US are also testing new delivery platforms. In December, Russia claimed that it had tested the Poseidon nuclear-capable super-torpedo, which President Vladimir Putin called ‘a great success.’ If the US also starts testing nuclear weapons, it could lead to a testing spiral that may draw others in and encourage some non-nuclear powers to consider nuclear testing. Debates continue around whether to build nuclear weapons in countries such as Japan and South Korea; and even Sweden and Germany are looking for options beyond the US nuclear umbrella. This could very well mean the end of nuclear non-proliferation. Therefore, it may be prudent to agree on a few early, practical steps to improve international nuclear stability.
