What is China doing in the South China Sea? China claims most of the South China Sea as its own, and it has territorial disputes with nearly all its neighbours over its maritime claims in the area. The claims include the Paracel Islands and the Spratlys as well as the Pratas Islands, the Scarborough Shoal and the Macclesfield Bank.

These claims have led to increased tensions with Vietnam, the Philippines, Malaysia, Taiwan and Brunei, through which €4.5 trillion in maritime trade passes every year.

Over the past few years, China has built artificial islands in the Spratly archipelago to press its claim. This week evidence emerged that Beijing has positioned surface-to-air missiles on Woody Island, part of the Paracel Islands chain just east of Vietnam.

China has reclaimed land at three locations in the Spratly Islands – the Subi, Mischief and Fiery Cross reefs, and it has built a 3,000m-long airstrip that can handle bombers. In the Paracel chain, China now operates one airfield at Woody Island with J-11BH/BHS fighters there.

Where does this figure in China's overall government policy? President Xi Jinping, who is also head of the Central Military Commission, has been modernising the military, with a big focus on building up the navy. The National People's Congress last year approved funding to expand its navy to "protect China's maritime interests". Chinese warships have taken part in anti-piracy patrols in the Gulf of Aden and in extracting nationals from conflict zones in Libya and Yemen.

The ocean was one of four “critical security domains”, alongside outer space, cyberspace and nuclear force, in a 9,000-word White Paper last year. The document signalled that China would shift its focus from a sole strategy of “offshore waters defence” to a combined one of “offshore waters defence and open seas protection”, which appears to include China’s ambitions in the South China Sea.

For his part, Xi rejects claims that China has expansionist ambitions.

“Expansionism refers to laying claims to land outside one’s own territory,” he said. “China has never done anything like that, so such doubts or accusations are unwarranted.”

What does the United States make of China's activities in the area? The US is keen to maintain its regional importance, particularly in the face of China's growing influence in Asia, and the US navy has called the land reclamation project the "Great Wall of Sand".

The Asia-Pacific region accounts for 40 per cent of the world’s population, 48 per cent of world trade, and 57 per cent of global output.

US Pacific fleet commander Adm Scott Swift has warned of an arms race in the region that could lead to conflict. The US navy has sent warships to sail near the islands. In October, a warship sailed within 12 nautical miles (22.24km) of the artificial island on a coral reef near the Spratlys. What does China make of the US stance? China has warned Washington against "escalation". The issue is hampering good relations between the two powers. Last year Xi Jinping had a tetchy visit to the US, during which the issue of rising tensions in the South China Sea was broached.

Messages were sent around on official feeds on the WeChat social network, which has hundreds of millions of users, saying the “US military . . . has invaded the South China Sea” and there were angry editorials in Chinese state media.

Last year, a US spy plane flew over the Spratly Islands, prompting warnings from the Chinese navy to leave, while China has sent ships to within 12 nautical miles of the Aleutian Islands off Alaska, which it said was a routine exercise after drills with Russia.

Longer term, evaluating how China is going to respond is difficult, but it is possible that it might step up its programme of reclaiming land and building military facilities there.

What are China's neighbours doing about it? The Philippines has asked the Permanent Court of Arbitration in the Hague to affirm its right to areas within 200 nautical miles of its coastline, under the terms of a UN convention.

However, China’s growing influence in the region, especially economic, means that many countries are taking a less strident approach to chastising the country than they might.