China is building more than 100 missile silos in a remote desert, analysis of satellite imagery suggests.
US researchers, from the James Martin Centre for Nonproliferation Studies at the Middlebury Institute of International Studies, said they discovered the site while studying satellite photos.
The study's findings, first reported by the Washington Post, identified 119 missile silos, likely to hold intercontinental ballistic missiles, being built in the desert of Gansu province.
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The site is spread over 1800 square kilometres and includes the building of underground bunkers, cable trenches, roads and a small military base, researcher Jeffrey Lewis said.
The layout is similar to existing nuclear ballistic missile launch sites in Inner Mongolia.
Expert analysis suggests China has built or is building at least 145.
"We believe China is expanding its nuclear forces in part to maintain a deterrent that can survive a US first strike in sufficient numbers to defeat US missile defences," Dr Lewis said.
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According to the Stockholm International Peace Research Institute, China has about 350 nuclear warheads, about 30 more than in 2020, and far fewer than the US or Russia.
Amid worsening relations with the US and its allies, China has been reluctant to cut its nuclear arsenal without similar limits on the US.
In April the chief of US nuclear forces had warned of an "breathtaking expansion" of Chinese nuclear weapons.
