A spectacular moment when disc-shaped clouds resembling an alien spaceship formed above a mountain in southern Vietnam went viral on social media in the country on Thursday.

Images of the rare natural phenomenon were captured at Ba Den Mountain in the southwestern province of Tay Ninh, which borders Ho Chi Minh City, by local resident Do Vinh Quan.

Quan said he took the pictures of the clouds at around 6:00 am on his way to work before sharing them on his social media account.

Some online users humorously described the image of clouds as a giant mushroom or an unidentified flying object (UFO). 

The natural phenomenon is known as lenticular clouds, according to Le Dinh Quyet, deputy head of the forecasting department at the Southern Center for Hydro-meteorological Forecasting.

They are dense, stationary clouds which are caused by sudden air movements and are often found near hills or mountains. 

As moist and stable air flows over a larger eddy, like those caused by mountains, and temperatures drop below the dew point, lenticular clouds can form.

The occurrence of lenticular clouds is not rare, according to Quyet, but the shape of a flying saucer is infrequent.

Quyet added that lenticular clouds are expected to form over Ba Den Mountain for the remainder of the month.

The flying saucer-shaped clouds recurred early on Friday morning, according to a photo provided to Tuoi Tre News by Ta Ngoc Anh, another local.

Standing at 986 meters above sea level, Ba Den Mountain in Tay Ninh Province has been dubbed the roof of Vietnam’s southern region. 

Viewed from a distance, the mountain stands out against the blue sky and is sometimes hidden behind clouds and fog.

From the base to the top of the mountain, visitors can stop by and explore temples, pagodas, caves, and towers, with local architecture – a mix of Buddhist and folklore culture - that attracts millions of visitors each year.

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