China is creating a 'great wall of sand' in the South China Sea, the US Navy has said. The latest huge land mass is 1.5 square miles (four square kilometres) in size and was created by dumping sand on live coral reefs, possibly damaging local ecosystems. But this is just one of several artificial islands China has been creating in the region - and the exact purpose of them is unknown. China is creating a 'great wall of sand' in the South China Sea, the US Navy has claimed. Five islands have already been made, with two more in development. This image shows the Johnson Reef on 25 February 2014, which has seen land added drastically over the last three years. A Chinese vessel is seen at the top . The large expanses of sand and concrete - the latest being Johnson Reef - are being built among the Spratly Islands in the South China Sea. China is creating the area by using dredging vessels to dig up sediment from the sea, and then dumping it on subermeged coral reefs to make islands, Ethan Rosen - a geopolitical researcher in China - explained. And experts have told MailOnline that the activities could be hugely damaging to local ecosystems. China has supposedly been carrying out the land reclamation in order to build airstrips and other structures in the region. Five islands in total have been built in this way, and two more are in development. Richard Dodge of the Nova Southeastern University Oceanographic Center, said: 'The activities described would appear to clearly both be greatly exceeding corals and coral reefs’ ability to cope and survive the excess sediments and turbidity.' He said that as the reefs were being covered by cement and landfill, this constituted 'outright destruction' of the buried coral reefs and associated habitats. 'Coral reefs are extremely globally and locally valuable both for the biodiversity and ecosystem they create but also for the tremendous services they provide in terms of food supply, cultural heritage, erosion prevention, recreation, tourism, and habitat for myriad other organisms,' he continued. 'Coral reefs worldwide are under extreme threat from changing climate and from local sources of land based pollution, over fishing, and coastal construction. 'The activities described would appear to represent an additional and severe threat to coral reef ecosystem health and sustainability.' Robert Nicholls, a Professor of Coastal Engineering at the University of Southampton, added: 'It is clearly destroying [coral reefs] at the local scale of the land claim and the environment. 'In the bigger scheme of things it is harder to be precise as these are small areas in a large area of reef.' Experts have told MailOnline that the activities could be hugely damaging to local ecosystems. China has supposedly been carrying out the land reclamation in order to build airstrips and other structures in the region. The extent of how much damage is being done is seen in this image . This photo released by the Philippine Department of Foreign Affairs, shows what the Johnson Reef looked like on 28 February 2013. A Chinese-made structure stands on the Johnson Reef, called Mabini by the Philippines and Chigua by China, in the Spratly Islands in the South China Sea . This photo, taken on 13 March 2012, shows what the Johnson Reef looked like before China started to build there. The Philippines has protested China's reclamation of land in the disputed reef in the South China Sea that can be used to build an airstrip or an offshore military base in the increasingly volatile region . Yesterday, the commander of the US Pacific Fleet - Admiral Harry Harris Jr - warned that the constructions were 'increasing regional tensions and the potential for miscalculation.' 'China is building artificial land by pumping sand on to live coral reefs - some of them submerged - and paving over them with concrete. China has now created over 4 square kilometers (1.5 square miles) of artificial landmass,' he said. Harris said the region is known for its beautiful natural islands, but 'in sharp contrast, China is creating a great wall of sand with dredges and bulldozers over the course of months.' China claims virtually all of the South China Sea, but the Philippines and other countries which have territorial disputes with China in the busy sea have been particularly concerned by the land reclamation projects. These have turned a number of previously submerged reefs in the Spratlys archipelago into artificial islands with buildings, runways and wharves. The islands could be used for military and other facilities to bolster China's territorial claims. The dispute centres around hundreds of tiny shoals, reefs and islets in the South China Sea known as the Spratlys and the Paracels. Several south Asian countries stake claim to the territory, though China tries to control the largest portion of the archipelago. Beijing has claimed its right to the collection of land masses is 2,000 years old which, they say, includes the islands in Chinese history. Taiwan supports its claim, and has its own airfield on the island of Taiping. Vietnamese officials say their government has ruled over the land since the 17th century whilst the Philippines, the closest geographically, says the islands belong to them. In 1974, Chinese forces seized the Paracels from Vietnam, killing 70 troops. There were further clashes between the two countries in 1988, with 60 Vietnamese soldiers killed. In 2012 China and the Philippines were embroiled in a lengthy maritime standoff over a Scarborough Shoal. The Filipino military employed its largest warship for the dispute over the stretch of water which they call Panatag. Upon boarding a Chinese military vessel for inspection, officials claimed they found live sharks, clams and illegal reef. Later, Vietnamese border agencies refused to stamp passports asserting Chinese sovereignty over a handful of the islands and in January it was claimed China would be taken to a UN tribunal to challenge its stake. China is creating the area by using dredging vessels to dig up sediment from the sea, and then dump it on subermeged reefs to make islands, Ethan Rosen - a geopolitical researcher in China - explained. Shown is an image of a dredging vessel in San Francisco, demonstrating how land can be moved from underwater . Harris said the pace of China's construction of artificial islands 'raises serious questions about Chinese intentions.' He said the US continues to urge all claimants to conform to the 2002 China-ASEAN Declaration of Conduct, in which the parties committed to 'exercise self-restraint in the conduct of activities that would complicate or escalate disputes and affect peace and stability.' 'How China proceeds will be a key indicator of whether the region is heading toward confrontation or cooperation,' he said. The US says it has a national interest in the peaceful resolution of the disputes in a region crucial for world trade. China says its territorial claims have a historical basis and objects to what it considers US meddling.
China is building artificial islands on coral reefs in the South China Sea .
Five have been built in the Spratly Islands - with two more in development .
The latest island is a huge 1.5 square miles (four square km) in size .
But experts told MailOnline the activities could be hugely damaging .