The world's second largest civil aviation market is set to an unprecedented takeoff, putting China second only to the U.S. in terms of civilian airports.

The PRC's air passenger transportation throughput, measured in revenue passenger-kilometers, will grow 8.4 percent annually during 2007-2026, according to the Asian Development Bank (ADB).

Air cargo transportation turnover, measured in freight ton-kilometers, will increase at an annual rate of 10.5 percent, it said.

As of 2006, the country had 146 civil airports in operation. By 2010, China plans to construct and expand 60 more airports, mostly in the western region.

Under the 11th Five-Year Plan, some $17.7 billion in capital expenditure is needed for civilian airports.

"The country currently has the second largest civil aviation market in the world, after the U.S.," said Sherwin Pu, investment specialist of ADB's Private Sector Operations Department.

"The demand for travel, for both work and leisure, is projected to increase at an unprecedented pace due to increased labor movement flexibility and disposable income growth," he said.

In its first foray into China's airport business, the ADB will put a $50 million equity investment from ADB in HNA Airport Holding (Group) Co. Ltd., a private company primarily investing in airports and their operations.