China has landed its first plane on an artificial island after completing one of three runways it has been constructing on the Spratly Islands.
The landing shows Beijing's facilities in the disputed region are being completed on schedule and military flights will inevitably follow, foreign officials and analysts said.
They said activity in the South China Sea could transform the region into a Beijing-controlled air defence zone.
China’s action resulted in concerns and protests from mutually interested countries in the region, with Vietnam launching a formal diplomatic protest.
Vietnam said the plane landed on Jan 2 and launched a formal diplomatic protest, while Philippines Foreign Ministry spokesman Charles Jose said Manila was planning to do the same. Both have claims to the area that overlap with China's.
"That's the fear, that China will be able take control of the South China Sea and it will affect the freedom of navigation and freedom of overflight," Jose told reporters.
Following the move, US Senator John McCain - chairman of the influential US Senate Armed Services Committee - expressed disapproval over Obama not ordering further "freedom of navigation" patrols.
The runway at Fiery Cross Reef is 3,000 metres (10,000 feet) long and is one of three China was constructing on artificial islands built up from seven reefs and atolls in the Spratlys archipelago.
Military landings on the islands were now "inevitable," said Leszek Buszynski, a visiting fellow at the Australian National University's Strategic and Defence Studies Centre.
"The next step will be, once they've tested it with several flights, they will bring down some of their fighter air power - SU-27s and SU-33's - and they will station them there permanently. That's what they're likely to do."
China says the islands will be used for coast guard activity and fishing research as well as to save travelling time between the Spratly islands and mainland China.