Satellite images show China is building an island on a reef in the disputed Spratly Islands large enough to accommodate its first offshore airstrip in the South China Sea, a leading defence publication has claimed.

The construction has stoked concern China may be converting disputed territory in the mineral-rich archipelago into military installations, adding to tensions over waters also claimed by Taiwan, Malaysia, the Philippines, Vietnam and Brunei. The building work flies in the face of US calls for a freeze in provocative activity in the South China Sea.