BEIJING -- Two civilian jets landed on the airstrip of a new island China built in the South China Sea, drawing more protests over China's activities in disputed waters.

The China Daily newspaper reported Thursday the planes made the two-hour flight to Fiery Cross Reef from Haikou on the southern island province of Hainan.

It said the test flights on Wednesday proved the runway's ability to safely handle large civilian aircraft. Photos showed one of the planes to be a China Southern Airlines Airbus A319-115.

An earlier test flight Saturday drew angry protests from Vietnam, Philippines and Japan.

China's building of seven islands by piling sand on reefs and atolls has been condemned by its neighbours and the United States, which accused China of raising tensions in an area where six governments maintain overlapping maritime territorial claims.

In Manila, visiting British Foreign Secretary Philip Hammond said freedom of navigation and overflight in the South China Sea was non-negotiable and urged rival governments to avoid provocative steps.

"They are red lines for us," Hammond said, adding that as a major trading nation, Britain expects to continue exercising those rights.

Vietnamese Foreign Ministry spokesman Le Hai Binh said in a statement that China's action seriously violated Vietnam's sovereignty and demanded China immediately stop and that it respect international law.

Philippine Foreign Secretary Albert del Rosario warned that China may next impose an air defence identification zone above the contested region, as it did over the East China Sea, and said such a move would be "unacceptable."

China has rejected calls for a halt in island construction, saying its claim of sovereignty over the entire area gives it the right to proceed as it wishes. It says the new islands are principally for civilian use but also help defend Chinese sovereignty.

China's robust assertions of its claims have sparked tense exchanges, mainly among China, Vietnam and the Philippines, over long-disputed and potentially oil- or gas-rich offshore territories also claimed by Taiwan, Malaysia and Brunei.

That's also creating new tensions with the U.S., which has refused to recognize the new islands as geographic features deserving of territorial waters and other aspects of sovereignty.

While Washington takes no formal position on the various sovereignty claims, it insists that disputes be settled peacefully and that freedom of navigation be maintained in waters through which more than 30 per cent of global trade passes.

Fiery Cross Reef is the largest of the seven new islands that in total compose more than 800 hectares (2,000 acres) of reclaimed land. Its 3-kilometre (10,000-foot) airstrip is long enough to handle any plane operated by the Chinese military.

Another runway is being built on Subi Reef, with signs of similar work underway on nearby Mischief Reef. If all are completed, China would possess four airstrips in all on its South China Sea island holdings.