The heavily contested South China Sea, part of the Pacific Ocean, is rich with natural resources.
Six neighbouring countries have also laid claims to the sea, which borders Vietnam, Brunei and the Philippines.
A BBC team flew over the disputed South China Sea islands in a US Navy plane, during which the plane was told to “leave immediately and keep far off” by the Chinese Navy.
The crew aboard the plane were unphased by the warning, something that has become a daily encounter.
“It’s a routine occurrence for us on these flights, it happens throughout the flight, where they come over and we just go back with our standard response and it really has no effect on any operations or anything we do,” said Lt Matt Johnston.
During the flight they approached an island built entirely by the Chinese government, called “Mischief Reef”.
It becomes clear the island had grown significantly since the BBC last took a flight over it in 2015.
The artificial island appears to now have radar domes, aircraft hangers and possibly somewhere to park missile launchers.
Beijing, China’s capital, continues to lay claims to the region’s sovereignty.