HONG KONG (UPDATED)- China's creation of artificial islands in the West Philippine Sea (South China Sea) is happening so fast that Beijing will be able to extend the range of its navy, air force, coastguard and fishing fleets before long, much to the alarm of rival claimants to the contested waters.

Reclamation work is well advanced on six reefs in the Spratly archipelago, according to recently published satellite photographs and Philippine officials. In addition, Manila said this month that Chinese dredgers had started reclaiming a seventh.

While the new islands won't overturn U.S. military superiority in the region, Chinese workers are building ports and fuel storage depots as well as possibly two airstrips that experts said would allow Beijing to project power deep into the maritime heart of Southeast Asia.

"These reclamations are bigger and more ambitious than we all thought," said one Western diplomat. "On many different levels it's going to be exceptionally difficult to counter China in the South China Sea as this develops."

China claims most of the potentially energy rich South China Sea, through which $5 trillion in ship-borne trade passes every year. The Philippines, Vietnam, Malaysia, Brunei and Taiwan also have overlapping claims.

All but Brunei have fortified bases in the Spratlys, which lie roughly 1,300 km (810 miles) from the Chinese mainland but much closer to the Southeast Asian claimants.

Beijing has rejected diplomatic protests by Manila and Hanoi and criticism from Washington over the reclamation, saying the work falls "within the scope of China's sovereignty".

The Philippines began expressing growing concern in mid-2014, in particular, accusing Beijing of building an airstrip on Johnson South Reef.

Satellite analysis published by IHS Jane's Defence Weekly this week showed a new installation being built on Hughes Reef. It described a "large facility" having been constructed on 75,000 square metres of sand reclaimed since August.

It also published images of Fiery Cross Reef, which now includes a reclaimed island more than 3 km (1.8 miles) long that experts said would likely become a runway.

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China to project power from artificial islands