In the past 18 months, China has been enthusiastically dredging sand from the bottom of the South China Sea and building artificial islands in disputed waters. During that period, according to Ashton Carter, US secretary of defence, Beijing has reclaimed more land than all the other claimants put together over the history of the dispute. True, Vietnam, the Philippines, Malaysia and Taiwan have all built islands to bolster their territorial claims. Yet Beijing’s actions dwarf those efforts in both speed and scale.

The exercise is being carried out in a state of secrecy. No one knows quite what China is up to nor what it hopes to achieve. The lack of transparency is unnerving given China’s territorial ambitions. With little or no basis in international law, it lays claim to virtually all of the South China Sea, asserting ownership of everything within a nine-dash line hugging the coast of the Philippines, Malaysia and Vietnam. One theory is that Beijing wants to build a runway in order to enforce an air defence identification zone over the entire sea. Beijing should desist from such an unnecessary provocation.

In the run-up to this weekend’s Shangri-La Dialogue, a regional security summit held in Singapore, Washington has begun to push back. This month, it flew a P-8 Poseidon aircraft — with a CNN television crew on board — over one of China’s new islands, eliciting a sharp warning from the Chinese navy. The US says it has detected artillery pieces and has reserved the right to sail warships within 12 miles of the newly created islands. This weekend, Mr Carter made it clear the US would “fly, sail and operate wherever international law allows” and said China’s act of “turning an underwater rock into an airfield” in no way conferred sovereign rights. Chinese Admiral Sun Jianguo responded that Beijing’s actions were “justified, legitimate and reasonable” and were intended to provide “international public services”. His words will bring little comfort to the Asian nations that feel threatened by China’s behaviour.