U.S. Warships Enter Disputed Waters of South China Sea.
An Australian warship has also joined with this.
The area is near waters claimed by both Vietnam and Malaysia as well as China.
China claims most of the energy-rich South China Sea, within a U-shaped "nine-dash line" on its maps.
But that is not recognised by its neighbours.
Vietnam recently protested after China said that China had established two administrative districts on the Paracel and Spratly islands in the disputed waters.
About
The South China Sea is a marginal sea.
It is a part of the Pacific Ocean, encompassing an area from the Karimata and Malacca straits to the Strait of Taiwan.
The nine-dash line refers to the claims by China in the South China Sea.
It includes the Paracel Islands, the Spratly Islands, the Pratas Islands, the Maccles field Bank and the Scarborough Shoal.
The claim encompasses the area of Chinese land reclamation known as the "Great Wall of Sand".