The sun shone red and the sky darkened to a foreboding orange and brown across parts of Britain on Monday, as Storm Ophelia brought dust from the Sahara and smoke from wild fires in southern Europe that filtered out certain wavelengths of sunlight.

Downgraded from a hurricane overnight, Ophelia caused two deaths in Ireland on Monday, where it was the worst storm in half a century.

Social media users shared pictures of ominous-looking clouds blocking out the sun, prompting London's Science Museum to joke on Twitter: "It's not the apocalypse!"

Many people expressed unease at the phenomenon, while others remarked it looked like something out of a science fiction movie -- with one wit predicting an alien invasion.

Clouds gather over a view of Westminster in central London, Britain, October 16, 2017. (EPA Photo)

The sky over Westminster turns orange as storm Ophelia brings dust from the Sahara, filtering the light over London, Britain, October 16, 2017. (REUTERS Photo)

The sky over Westminster turns orange as storm Ophelia brings dust from the Sahara, filtering the light over London, Britain, October 16, 2017. (REUTERS Photo)

The sun is seen after dawn after the Met Office reported that storm Ophelia has drawn dust north from the Sahara, near Exeter, Britain October 16, 2017. (REUTERS Photo)

People walk through Canary Wharf while the sky overhead turns red as dust from the Sahara carried by storm Ophelia filters sunlight over London, Britain, October 16, 2017. (REUTERS Photo)

Skies over London's financial centre Canary Wharf are given a yellow glow as dust from the Sahara desert and wild fires in Spain, blown across the city by Storm Ophelia, filters out the light, in London, Britain October 16, 2017. (REUTERS Photo)

Office workers stand on their balcony to photograph the darkened sky over London on October 16, 2017 caused by warm air and dust swept up by storm Ophelia. (AFP Photo)

A plane flies past the Shard in central London, as the sky takes on an unusual orange colour caused by Hurricane Ophelia Monday Oct. 16, 2017. (AP Photo)

Hyde Park is bathed in a dull sepia light from the sky in London, Monday, Oct. 16, 2017. (AP Photo)

The unusual hue of the daylight sky was thought to be due to the remnants of Hurricane Orphelia dragging in tropical air and dust from the Sahara. (AP Photo)

The prospect of the impending end of the world also drew inevitable comparisons with Britain's increasingly tortured withdrawal from the EU.

"Huh, turns out Remoaners were right... #BrexitApocalpyse #YellowSky," tweeted one of the leading Brexit campaign groups, Leave.EU.

Met Office forecaster Grahame Madge said the unusual effect was caused by Ophelia, the hurricane now downgraded to a violent storm which battered Ireland on Monday.

"On the eastern side of the low pressure system air is coming up in the southern direction. Air is being pulled from southern Europe and Africa and that air contains a lot of dust," he said.

"So it's most likely the appearance of sunset at midday is caused by the particles scattering the light and giving the appearance of a red sun.

"It's certainly spectacular at the moment and quite a talking point, we've had a lot of calls about it."

As Ophelia has come up from the Azores, the storm has picked up Saharan dust from North Africa and picked up dust from wild fires in Spain and Portugal," a spokeswoman for Britain's Met Office also said.

"This yellowish hue is from the dust that is high up in the atmosphere and the blue element of the sunlight is scattered by the dust but the red element gets through so the sun appears redder and you get this sort of yellowish tinge," she said.