It looks like any other city skyline with skyscrapers, a few mountains and trees -- except it isn't real.

The giant mirage appeared across the skyline in East China earlier this month after heavy rainfall and humid conditions covered the Xin’an River.

As mist settled over the river at dusk, tall buildings appeared to rise from nowhere, leading residents in nearby Huanshan City to speculate that the vision may be a "vortex" to a lost civilization.

"It's really amazing, it looks like a scene in a movie, in a fairyland," one resident told UK news channel ITN. The mysterious city had vanished just as quickly as it had come.

Scientists have quashed the vortex theory, however, with a far simpler explanation for the incredible sight. They believe it may have been a mirage, caused when moisture in the air becomes warmer than the temperature of the water below.

When rays of sunlight cross from the colder air into the warmer air they are refracted or bent -- creating a reflection in the air that looks similar to a reflection in water. It's a common sight for many travellers to wet areas. But one is more likely to encounter puddles of water that disappear when you get close than entire cities floating on rivers.