China is helping the US navy to search for an American marine who may have gone overboard in the South China Sea – a rare instance of cooperation in the disputed waters. The Chinese Ministry of Defence said on Thursday that its warship Liuzhou, from the South China Sea Fleet, was working with the US to find the missing marine “in the spirit of humanitarianism”. The marine was reported to have gone overboard from the destroyer USS Stethem around 9am on Tuesday, according to the US Navy’s Pacific Fleet. Multiple searches were conducted inside the ship, but the man has not yet been found, it said. The Chinese ministry said the marine reportedly fell into the water more than 100 nautical miles from Scarborough Shoal, a rocky formation in the South China Sea claimed by China, the Philippines and Taiwan. Xi personally behind island-building in the South China Sea China lays claim to almost all of the South China Sea, creating territorial disputes with its neighbours. The country has sought to back these claims through island-building projects and naval patrols in the disputed waters. While the US has no territorial claims in the area, it has engaged in “freedom of navigation” missions to challenge China’s claims. China said its cooperation in the search for the US marine was in line with the “Code for Unplanned Encounters at Sea”, an agreement between 25 countries – including China and the US – to reduce and prevent escalation between the countries’ navies. “The adoption of this code further advances naval exchange between countries – effectively controlling maritime crises, reducing misjudgments, avoiding interference or collisions when engaging in high sea activities, effectively maintaining regional maritime safety and stability,” Zhang Junshe, a researcher at the PLA Chinese Naval Research Institute, told the mainland paper Legal Evening News . The Liuzhou warship involved in the search is one of the “nine brothers” in the Chinese navy’s destroyer attachment in the sea. It has an air defence missile system that can destroy targets up to 50 kilometres away, and is one of the navy’s most advanced vessels. China plans station on disputed South China Sea shoal It was also one of the two ships that the Chinese defence ministry said “warned and expelled” a US destroyer in May near Mischief Reef, an island claimed by China, Taiwan, Vietnam and the Philippines.