Strange things are happening in the South China Sea. In the past 18 months, Beijing has reclaimed 2,000 acres of land, converting several submerged reefs and rocks into fully fledged “islands”. Beijing’s land-reclamation efforts have dwarfed those of other countries, notably the Philippines and Vietnam, which have rival claims to the nearby Spratly Islands. China is also constructing piers, harbours and multistorey buildings (though there is no Fifa football stadium yet). On Fiery Cross Reef, in the Spratly Islands, it has built a 3km runway capable of handling all the military aircraft at Beijing’s disposal.

The splurge of activity has set alarm bells ringing. This month, in a speech in Tokyo, Benigno “Noynoy” Aquino, president of the Philippines, likened China’s activity to Nazi Germany’s annexation of Czechoslovakia. Ashton Carter, US defence secretary, called Chinese actions “out of step” with international norms. The US, he said, would “fly, sail and operate” wherever international law allowed. He explicitly denied that the act of “turning an underwater rock into an airfield” conferred any rights of sovereignty or restricted any other nation’s right of sea or air passage. China and other claimants, he said, should immediately cease all land reclamation.

That begs the question: what is the US going to do about it? The short answer may be not much. The US continues to fly military planes near the new islands. It and other nations are stepping up military co-operation in an effort to show a united front. Yet China’s island reclamation programme has proceeded apace. Mr Carter’s words sound like President Barack Obama’s “red line” in Syria. If Beijing continues to call Washington’s bluff, the truth will be out: the US speaks loudly but carries a small stick.