Washington - China has ramped up its land reclamation efforts in the South China Sea this year, building artificial islands at an unprecedented pace to bolster its territorial claims in the disputed area, United States officials said.

The rapid construction of artificial islands in the strategic waters amounts to about 800ha of reclaimed land, 75 per cent of it built in the last five months, officials said.

"China has expanded the acreage on the outposts it occupies by some 400 times," said a US defence official.

The US did not endorse land reclamation by any of the countries with territorial claims in the South China Sea, but "the pace and scale of China's land reclamation in recent years dwarfs that of any other claimant", the official said.

The South China Sea is home to strategically vital shipping lanes and is believed to be rich in oil and gas. Washington is concerned that China's efforts carry a military dimension that could undermine the US' naval and economic powers in the Pacific.

US officials released the reclamation estimate as the Pentagon issued its annual report to Congress on the state of China's military, which repeated accusations that Beijing was staging cyber attacks to get information on US defence programmes.

The report also warned that China has made major strides with a range of satellites as well as anti-satellite jammers, saying it now had "the most dynamic space programme in the world today".

China blasted the US report yesterday, accusing it of distorting facts.

"The US Defence Department's report on China's military and security development situation distorts facts and continues to play up the 'China military threat' cliche," Chinese defence ministry spokesman Geng Yansheng said.

He made no direct mention of land reclamation in the South China Sea, but said China was justified in upholding its sovereignty in the area.

Previous reports have noted China's focus on cyber and space weapons, but this year's document included a special section on the country's massive dredging and island building in the strategic South China Sea.

At four reclamation sites, China has moved from dredging operations to "infrastructure development" that could include harbours, communications and surveillance systems, logistics support and "at least one airfield", the report said.

Unlike other countries making claims in the area, China does not have an airfield or "secure docking" at its outposts and the reclamation operations may be aimed at ending that disparity, it said.

The Pentagon report covered a period ending last December and it said China had reclaimed 202ha in the disputed waters up to that point. But since then, China has conducted reclamation covering 607ha, officials said.

China has repeatedly defended its construction work as taking place within its own territory, and said it intended to help with maritime search and rescue, navigation and research.

In response to the Philippines' earlier accusation that China's reclamation has breached a 2002 joint declaration, China's Foreign Ministry spokesman Hua Chunying on Friday urged Manila to stop hyping China's construction work.

She said that the Declaration on the Conduct of Parties in the South China Sea (DOC) is not a tool for the Philippines to whitewash its wrongdoings.

"The Philippines' willful abuse and distortion of the DOC is in itself a breach and damage to the DOC," Ms Hua said.

China has accused Vietnam, the Philippines and other claimants of carrying out their own illegal building work.

AFP, Xinhua