China is “creating a great wall of sand” through land reclamation in the South China Sea, causing serious concerns about its territorial intentions, the commander of the US Pacific fleet said on Tuesday.

Admiral Harry Harris Jr told a naval conference in Australia that competing territorial claims by several nations in the South China Sea are “increasing regional tensions and the potential for miscalculation”.

“But what’s really drawing a lot of concern in the here and now is the unprecedented land reclamation currently being conducted by China,” he said.

“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. The Philippines and other countries that have territorial disputes with China in the busy sea have been particularly concerned by the land reclamation projects, which 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.

Harris said the pace of China’s construction of artificial islands “raises serious questions about Chinese intentions”.

He said the United States 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.

Harris said the United States is on track to reposition 60% of its navy to the Pacific fleet by 2020.

“By maintaining a capable and credible forward presence in the region, we’re able to improve our ability to maintain stability and security,” he said. “If any crisis does break out, we’re better positioned to quickly respond.”