This is the spectacular moment a cap cloud formed over a mountain in northern Thailand.

Time-lapse footage shows the pileus, also known as a scarf cloud or cap cloud, covering the summit of Doi Luang Chiang Dao in Chiang Mai on December 14.

The phenomenon lasted for more than an hour, with tourists pulling out their phones to record the rare sight.

A pileus is a small, horizontal, lenticular cloud that appears above a cumulus or cumulonimbus cloud.

They form when strong updrafts push moist air to higher altitudes, causing the air to cool rapidly and condense into ice crystals.

Cap clouds usually form in drier air, which inhibits vertical growth and instead creates the smooth, horizontal lens shape over elevated terrain.