Under the leadership of the Communist party, China is building what an American admiral, Harry Harris, calls a “great wall of sand” in the strategically important waterways of the South China Sea.

The Chinese are dredging the sea bed to transform a few reefs and rocks in the Spratly group of islands and atolls – which they claim – into man-made islands with a runway that can support military flights. This has caused great concern among their neighbours. The Chinese government rejects international criticisms, asserts its sovereign right to build on the islands, and demands that American naval surveillance aircraft overflying the new islands leave the Chinese air control zone immediately. There are also reports that China has begun to put heavy weapons on one of them.

While one of the new islands looks like an unsinkable aircraft carrier in the making, it is unlikely to be built to project Chinese air power. In the age of long-range missiles and precision weapons, immovable aircraft carriers are easy targets. What really motivates the Chinese government is something more strategic.

By transforming rocks into islands, the Chinese government is creating a reality on the ground in asserting its sovereignty over these disputed rocks and laying the ground to claim the territorial waters around them. The Chinese statement that they will eventually allow others to use facilities on the islands for disaster relief or rescue operations is significant. To take advantage of them, users will no doubt need to acknowledge Chinese sovereignty.

The fact that the United Nations convention on the law of the sea is clear on what constitutes an island with territorial water – which should exclude such man-made structures – is not deemed an insurmountable obstacle in China. The ruling Communist party has never allowed the law to restrict what it can do. Even in the international community it has a record of successfully imposing its will on other states, notwithstanding the norm. The classic case is Taiwan’s international status.

Taiwan has a permanent population, a defined territory, a democratically elected government and the capacity to enter into relations with other states, and thus meets all the criteria for statehood under the Montevideo Convention of 1934. It has also never come under the jurisdiction of the People’s Republic of China. But the Chinese government lays claim to Taiwan and insists on other states not violating its “one China principle”.

By dogged insistence and skilful use of leverage, it has successfully persuaded most nations not to challenge its assertion that Taiwan is not a country but a “renegade province of China”. It has reason to believe it can achieve the same with the Spratly islands.

This is exactly why Vietnam and the Philippines, which also claim the same islets, are deeply concerned. Most other states in east Asia also find the Chinese move discomfiting. It is the apparent casualness with which China asserts its claims regardless of other conflicting claims that is disconcerting. What will China do next?

In its rush to secure this crucial waterway for Chinese shipping, Beijing is seeking to strengthen its efforts to build a new “maritime silk road” through the South China Sea and the Indian Ocean to east Africa and the Mediterranean. But it is counter-productive. For the maritime silk road idea to succeed, it must be embraced by China’s maritime neighbours. They need to feel reassured that the Chinese are not aggressive. The island-building delivers the opposite effect.

Maritime powers with no involvement in the disputes, such as the US and Australia, are also concerned as the Chinese move is a big step forward to laying claim to territorial waters around these man-made islands. If China should successfully claim all of the Spratly islands, it would transform most of the South China Sea, one of the most important maritime routes in the world, into a “Chinese lake”.

The US has sent a naval aircraft and may dispatch ships close to the new islands to demonstrate that it does not acknowledge that any change of status under international law has taken place. It needs to do so to protect the freedom of navigation, but it is a dangerous game that is being played – by both sides.

Steve Tsang is professor of contemporary Chinese studies at the University of Nottingham