The Beidou satellite, which western observers have said may also have military uses, lifted off from the Xichang launching site in southwestern Sichuan province 34 minutes after midnight, Xinhua news agency said.

It was transported on board a Long March 3-A carrier rocket, just like the two previous satellites in the system, which were launched in late 2000.

With the three satellites in orbit, China now has a complete system for all-weather navigation and positioning information, serving as a "radio beacon in outer space," Xinhua said.

The system will play a key econimic role, providing services in fields such as transportation, telecommunications and meteorology and helping in preventing forest fires as well as in police work, it said.

However, the Beidou navigation system is also expected to have military uses capable of improving the accuracy of Chinese missiles, according to Western military sources.

China has been seeking to build a satellite navigation system accurate enough to be incorporated into precision munitions, similar to the smart weaponry that has helped the United States to victory in recent wars.

As part of its effort to enter the space age, China has said repeatedly it plans to send its first human into space on board a craft called Shenzhou V some time this fall.

China has so far launched four unmanned spaceflights, the last of which, Shenzhou IV, returned to earth in January after 162 hours in orbit seen as the final dress rehearsal before a manned mission.

With a successful manned space flight, China would become only the third country to send a human into orbit following the former Soviet Union and the United States.

SPACE.WIRE