Tourists stunned by rare 'cloud waterfall' phenomenon spotted in China

A rare cloud phenomenon has been captured on camera over China.

The so-called 'cloud waterfall' can only occur with very specific atmospheric conditions, but tourists in the Chongqing region were treated to the natural phenomenon last week.

It happens when a large body of fog forms at the top of a peak, then slowly sinks downward as it travels over the edge.

Watch the video above.

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The video was filmed on May 5, in Chongqing, southern China.

The fog which gathers at the top of the mountain is dense enough - compared to the surrounding air - that it 'flows' over the edge and into the valley below in a way that looks like water.

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For a cloud waterfall to form, there must be the exact right combination of conditions and location.

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There needs to be the right altitude and temperature for clouds to form, the fog must be dense enough that it stays low to the ground, and there needs to be a slight wind to waft the fog over the cliff.

Cloud waterfalls are often seen on sea cliffs, and have been spotted here in Australia, too.

They are sometimes seen coming off the Otways in Victoria, flowing over the waters of Bass Strait.