The Gunsa Airport in southwest China's Tibet Autonomous Region is expected to start operation on July 1, 2010, to become the fourth civil airport on the "Roof of the World", local authorities said Tuesday.

The parking apron, its 4,500-meter-long runway as well as meteorological radars have been completed, said Hu Jinfa, head of the airport project headquarters.

The airport in Ngari Prefecture, more than 4,000 meters above sea level, will have an annual throughput capacity of 120,000 passengers by 2020. Test flights were conducted successfully from October 13 to 18, Hu said.

China Southwest Airlines will operate scheduled flights between Ngari and Lhasa and Xinjiang Uygur Autonomous Region.

Construction began in May 2007 and is expected to cost 1.647 billion yuan ($241.22 million).

Gunsa Airport is located in a relatively flat area compared with other airports in Tibet, said Hu.

"Only five months every year are suitable for construction work because of altitude sickness," said Hu. "We took shifts to work around the clock in these five months."

Ngari sits 4,500 meters above sea level in the northwest of Tibet, 1,600 kilometers from the regional capital Lhasa. The airport will help facilitate exchanges of personnel and logistics between Ngari and other places, said Dawa Tashi, the prefecture head.

The other airports in Tibet are Gonggar Airport in Lhasa, Bamda Airport in Qamdo Prefecture and Nyingchi Airport.