People left terrified after seeing 'tsunami cloud' on British holiday hotspot beach

Beachgoers were left baffled after their sunbathing sessions were suddenly interrupted by this terrifying display in the sky.

In scenes which wouldn't look out of place in an apocalyptic film, an ominous cloud resembling a towering tidal wave engulfed the Portuguese coast earlier this week.

It's safe to say that anyone who dozed off for a cheeky siesta on the sand would have absolutely sh*t themselves while waking up to this shocking sight.

Locals and tourists alike have taken to social media to share their accounts of what happened when the huge wall of rolling clouds billowed over them on the beach.

Discussing the terrifying moment the coastline was engulfed by the bizarre weather phenomenon, one person said in a Reddit thread that 'people were genuinely fearful.'

Another added: "We saw this yesterday in Ericeira. Came right over us. Got really windy and cold."

A third wrote: "I’m from Portugal I was at a beach where it happened. That s**t looked like something from a horror movie. Winds started to blow rapidly and strong."

The extraordinary display in the sky left people 'genuinely fearful', according to one beachgoer (Reddit)

And a fourth dubbed it the 'scariest horizon' they have ever seen, adding: "The contrast with the sliver lining from the clouds beside the darkness of the water is so eerie. Almost reminds me of a photo of a black hole."

Footage which is said to have been taken on a beach in the coastal city of Figueira da Foz was shared in the Reddit thread, showing stunned sun worshippers weighing up what on earth is going on.

A few brave swimmers remained in the water despite the dangerous-looking cloud making its way towards them, while the waves remained quite calm considering.

But the majority of people on the beach opted to get themselves on dry land, given that the rolling clouds were a dead ringer for the wall of water, which makes its way towards land during tsunamis.

That's why this unique weather phenomenon is often referred to as a 'tsunami cloud', rather than their official name, which is an 'arcus cloud.'

According to the Met Office, these are 'low-level, wide ranging clouds' which typically rear their head during a powerful thunderstorm.

The weather phenomenon was seen throughout the southern side of the country (ARTHUR CARVALHO/AFP via Getty Images)

It explains: "Arcus clouds are spectacular low-level, long and thin clouds associated with powerful thunderstorms. They are sometimes seen beneath Cumulonimbus clouds.

"Shelf clouds are attached to the storm cloud, whereas Roll clouds are a horizontal column separated from the storm cloud."

The aforementioned cloud varieties are different types of arcus clouds, according to the Met Office.

Explaining how they form, it goes on: "When a cold downdraft from a cumulonimbus cloud reaches the ground, the cold air may spread rapidly along the ground, pushing existing warm moist air upwards.

"As this air rises, water vapour condenses into the patterns associated with Arcus clouds. The new cloud may roll if it experiences different wind directions above and below."

The scary weather display is believed to be a result of the heatwave currently gripping Europe, as temperatures have been topping 46C in parts of Portugal at the minute.

The nation's meteorological agency, IPMA, said it had noted the 'existence of a disturbed flow, with waves within the atmosphere, known as internal gravity waves, particularly in a low layer of the atmosphere.'

Back in 1999, people in the Algarve believed a gigantic wave was heading straight for them when a rolling cloud cropped up in the sky, prompting the evacuation of beaches in the south of the country, the BBC reported.

However, it turned out to be nothing more of an optical illusion - which isn't dangerous, despite the eerie appearance of it.

Reddit users who chimed in on the thread from the safety of their own homes said they couldn't believe their eyes after watching the footage from Figueira da Foz.

One person said: "Just watched this...Fuuuuuuuu I'd be running."

A second commented: "Imagine nodding off on a beach towel, minding your own business and getting woken up to this."

A third pointed out: "The uniform shape is a little unnerving."

A fourth said: "That looks apocalyptic!"

And a fifth added: "I'm half expecting a city sized spaceship to come bursting through."