Google maps have revealed vast structures in China's remote Gobi Desert, sparking furious internet speculation that they may have some military link.
The structures are not far from Jiuquan, the headquarters for China's space program.
The structures include reflective rectangles up to 1.5km long.
Other pictures show enormous concentric circles radiating on the ground, with three jets parked at their centre, London's Daily Telegraph newspaper reports.
They are located on the borders of Gansu province and Xinjiang in northwestern China.
A 2007 image shows orange blocks arranged in a circle, but more recent images reveal that some of them have been scattered from the original site.
Ding Xin military airbase is about 640km away and Lop Nur, the sscene of nuclear tests in the 1960s and again in 1995 is also about 640km away.
Tim Ripley, a defence expert from Jane's Defence Weekly, told The Daily Telegraph the structures were similar to grids in Area 51, the secret US military test base in Nevada.
"It looks like our own Area 51," said one commenter on Baidu, a Chinese website. "Can it be an alien base," asked another.