THITU ISLAND, South China Sea (Reuters) - As the Philippine military C-130 transport plane made its approach to the country's most precious outpost in the disputed South China Sea on Monday, it flew past a reef which China is quickly turning into an island.
At least two cranes and two dredgers were visible on Subi Reef from the plane taking local and foreign reporters on a rare trip to Thitu island.
China's reclamation around seven reefs in the Spratly archipelago of the South China Sea is making Philippine islands such as this, known internationally as Thitu but called Pagasa in the Philippines, vulnerable, said Philippine military officials and security experts.
"In the last two years we have seen rapid development. They are getting closer to us. It's a threat," Major Ferdinand Atos, the highest-ranking soldier on Thitu, told reporters after the plane made a bumpy landing on the island's makeshift runway.
Subi Reef lies a mere 14 nautical miles from Thitu, its lights visible at night, Philippine officials said.
Atos said Chinese patrol ships had not tried to come close to Thitu, which is surrounded by shallow water.
But Ian Storey, a South China Sea expert at Singapore's Institute of South East Asian Studies, said the Philippines might struggle to sustain its holdings on Thitu and elsewhere in the Spratlys.
"Once (China) has all its facilities up and running, it will put the Philippines in a much more difficult position," Storey said. "The Chinese will be able to harass Philippine coastguard and naval vessels on a more regular basis ... they could try to impose blockades on other Philippine-occupied atolls, including Pagasa."
China recently warned Philippine air force and navy planes at least six times to leave areas around the Spratlys, the Philippine commander responsible for the region said last week.
Beijing claims sovereignty over most of the South China Sea, through which $5 trillion in ship-borne trade passes every year. The Philippines, Vietnam, Malaysia, Taiwan and Brunei also have overlapping claims.
Last month, China offered a detailed defense of its reclamation work, saying the new islands would provide civilian services such as weather forecasting and search and rescue facilities that would benefit other countries.
It has also accused other claimants, including the Philippines, of undertaking major reclamation work.
China's Foreign Ministry did not immediately respond to a request for comment on the trip by reporters to Thitu, which was organized by the Philippine military.
The coral-fringed Thitu, some 280 nautical miles from the Philippines, is the biggest island occupied by Manila in the contested region.
The 37-hectare (91-acre) island boasts fresh water, a small number of Philippine troops and a civilian population of about 100 people who take advantage of government subsidies to live here.
There is little sign of any upgrading.
The runway is no more than an unpaved track dotted with tufts of grass. Blue ocean water washes over one end while erosion is eating away at other sections.
The only sign that the island hosts a military base are two 40 mm anti-aircraft guns on opposite sides of the runway.
Thitu needs a proper wharf to spur tourism and fisheries, said Eugenio Bito-onon, mayor of Kalayaan, a municipality in the island province of Palawan that administers the island.
The military had developed a plan to upgrade the nine islands and reefs it holds in the Spratlys.
But those plans were put on ice after the Philippines filed a case with a U.N. tribunal in The Hague in 2013, challenging China's claims in the South China Sea. China has refused to take part in the arbitration case, which has yet to be heard.
China's creation of artificial islands is happening so fast that Beijing will be able to extend the range of its navy, air force and coastguard before long, experts say.
Dredging at Subi Reef showed a series of landmasses being created that, if joined together, would provide enough land for a 3,000-metre (3,281-yard) airstrip, IHS Janes Defence Weekly said last month.
China was building choke points in the Spratlys, Philippine military chief General Gregorio Catapang said last month, referring to reclamation that would narrow the room for Philippine vessels to move at sea.
"It will be a challenge for us to bring supplies and rotate our troops in the disputed area," he told reporters at the time.
On Monday while on Thitu, Catapang was more guarded when asked about the presence of Chinese vessels in the Spratlys.
"We don't see them as a threat, we should demilitarize this area," he said.
Joely Mendoza, 44, a mother of nine, said she had lived on Thitu for the past year. She was not afraid of the Chinese navy because its boats did not approach the island, she said.
"If the Chinese invade us here then we will just leave," Mendoza added.
Additional reporting by Greg Torode in HONG KONG; Writing by Dean Yates; Editing by Mike Collett-White