Some US naval commanders have expressed disagreement with the Obama administration regarding its stance on the raging territorial dispute in the South China Sea pitting regional powerhouse China against its small neighbours, including the Philippines, a staunch US ally.

The commanders want US Navy ships to sail right into the disputed territory to exercise freedom of navigation but have received orders from Washington not to do so as administration officials and diplomats try to manage a delicate phase in US-China relations.

To make it clear that the US rejects China's territorial claims in the area, US military officials and some members of Congress want the US to send warships within the 12 miles of China's man-made islands in the South China Sea.

The officials said US inaction would show that Washington is accepting China's destabilising moves in the region, which are viewed as a serious threat by the Philippines, Vietnam and Japan, another staunch US ally.

"We continue to restrict our Navy from operating within a 12 nautical mile zone of China's reclaimed islands, a dangerous mistake that grants de facto recognition of China's man-made sovereignty claims," said Sen. John McCain, the Republican chairman of the Armed Services Committee.

The territorial dispute in the contested waters also has implications in the global economy as the part of the sea claimed by China is the route used to ship goods from Asia to the rest of the world and vice versa.

China has created about 3,000 acres of new land over the last 18 months and has positioned artillery, built aircraft runways, constructed buildings, and placed radars and other equipment, said the Pentagon.

"China is changing the facts on the ground, literally, by essentially building man-made islands on top of coral reefs, rocks and shoals," said Adm. Harry Harris, chief of the US Pacific Command, at the recent Aspen Security Forum.

"I believe that China's actions to enforce its claims within the South China Sea could have far-reaching consequences for our own security and economy, by disrupting the international rules and norms that have supported the global community for decades," Harris warned.

China hit back on Thursday, saying it is the US that is "militarising" the South China Sea.

"China is extremely concerned at the United States' pushing of the militarisation of the South China Sea region," Defence Ministry spokesman Yang Yujun was quoted as saying. "Recently they have further increased military alliances and their military presence, frequently holding joint drills."