The recent flight of two US B-52 bombers near disputed islands in the South China Sea was an act a "serious military provocation," according to China's Defence Ministry today.

"Chinese armed forces will take whatever measures necessary to safeguard China's national sovereignty and security as well as peace and stability of the region," the ministry warned in an online statement on its website today.

The Dec 10 flyby near the Nansha Islands was "a serious military provocation, creating complex conditions in the South China Sea and even militarisation in the region," the statement said.

The ministry demanded Washington immediately take measures to prevent repeats of such incidents.

"Such actions have severely threatened the safety of Chinese personnel and facilities, as well as peace and stability of the region," it said.

A US official was quoted on Dec 11 as saying two bombers flew within 12 nautical miles of China's manmade islands near the Spratly Islands - the Nansha Islands in Chinese - on Nov 8-9, not Dec 10 as alleged by the Chinese side.

The ministry statement did not mention a November flight.

Many regional countries - including the Philippines and Vietnam - deny China's claim to most of the South China Sea, but Beijing has rapidly reclaimed land and expanded the islets to build airports, runways and other constructions.

The Chinese military contacted the bombers telling them to "get away from our islands," Washington-based newspaper The Hill quoted an unnamed US official as saying on Dec 11. The bombers did not comply, he added.

Pentagon spokesperson Bill Urban confirmed the flights, but told reporters that the bombers did not go within 12 nautical miles (22 kilometres) of any islands.

This is the limit of a country's sovereign territory in the sea, although it does not apply to submerged reefs or artificial installations built on them.

In recent weeks, the US has sailed two warships, including one carrying US Defence Secretary Ashton Carter, through the South China Sea in what the Pentagon describes as "freedom of navigation" operations.

China has described such sailbys in the sea - a major shipping route also thought to be rich in mineral resources - as "illegal."

The US commander in the Pacific, Admiral Harry Harris, said during a visit to Beijing earlier this month that "our military will continue to fly, sail, and operate whenever and wherever international law allows. The South China Sea is not - and will not be - an exception."

- dpa