China has built a satellite relay station in a group of islands in the South China Sea which are also claimed by Vietnam.
The official Xinhua newsagency said the installation on the Paracel XishaIslands would help China expand its security communications network and step up its fight against gun and drug smuggling.
China has also erected phone boxes on other islands the neighbouring Macclesfield Islands and further south in the Spratleys to which Vietnam, Brunei, Malaysia, the Philippines and Tawian all have claims.
Correspondents say any development on the islands -- some of which are thought to lie over important mineral and oil deposits -- are likely to be watched closely in the region.
From the newsroom of the BBC World Service