Stunning new aerial photographs have revealed the advances China has made "reclaiming" unpopulated islands and atolls in the disputed South China Sea.
China's claim to the patch of sea -- marked by a vague nine dash line -- has sparked ongoing tensions with countries in the region, as well as the U.S.
The South China Sea is a major trading seaway that sees trillions of dollars worth of goods pass through it each year.
China has been "reclaiming" unpopulated islands and atolls since 2014, adding buildings and other infrastructure, including runways.
In October a U.S. navy warship sailed near islands claimed by China in an attempt to counter what Washington sees as Beijing's efforts to limit freedom of navigation in the strategic waters.
The guided-missile destroyer USS Decatur challenged "excessive maritime claims" near the Paracel Islands, among a string of islets, reefs and shoals over which China has territorial disputes with its neighbours, U.S. officials told Reuters.
China this week said tensions in the South China Sea have eased because of "friendly cooperation" with the Philippines and other Southeast Asian nations.
James Woolsey, a former CIA director under president Bill Clinton and an advisor to U.S. President-elect Donald Trump, has said the U.S. won't abandon its Asian allies to China's "overreach."
"The U.S. sees itself as the holder of the balance of power in Asia and is likely to remain quite determined to protect its allies against Chinese overreach," he wrote in the South China Post last week.