China has made significant progress at three sites, suspected to be missile silo fields, which have western experts concerned. The three sites are located near Yumen, Hami and Ordos in north-central China.

Their progress is being monitored by Federation of American Scientists (FAS), a US-based non-partisan policy think tank. They have studied the progress at the three missile sites through commercial satellite images provided by Planet Labs and Maxar Technologies.

These images offer the most detailed pictures yet of the three sites, where FAS believes China is constructing 300 new missile silos.

The FAS researchers believe that the pace of construction gives them confidence that they are related to Chinese military’s modernisation programme. The progress has been reported almost on a weekly basis, said FAS.

“For China, this is an unprecedented nuclear buildup,” Matt Korda and Hans M Kristensen, the authors of FAS report said on Tuesday, adding that is raises questions and uncertainty about China’s minimum nuclear deterrent and policies.

The authors, however, added, “The apparent missile silo fields are still many years away from becoming fully operational and it remains to be seen how China will arm and operate them.”

Both Korda and Kristensen fear the rapid pace at which the silos are being constructed could increase nuclear competition and fuel worst-case planning in other nuclear weapon states.

The first silo field was discovered in June this year. Another report a second field was discovered in July, prompting the US Strategic Command to tweet about “the growing threat the world faces and the veil of secrecy that surrounds it”.

FAS had then said that these sites signify “the most significant expansion of the Chinese nuclear arsenal ever”. It added that this is the most extensive silo construction since the US and Soviet missile silo construction during the Cold War.