Rare 'blood rain' could hit the UK after dust from the Sahara crossed the Mediterranean and caused skies to glow orange.
The startling weather phenomenon is when high concentrations of red dust mix with rain, giving the appearance of blood falling from the sky.
Saharan dust was kicked up by Storm Celia as a mass of hot air moved across Europe, including parts of Spain and Switzerland, as residents photographed the eerie event.
The dust cloud, which is 2km above ground level, could fall during showers in the southern parts of the UK on Wednesday afternoon (March 16), the Met Office has predicted.
Spanish officials have issued extremely poor air quality ratings and experts have now warned it's making its way to the UK, The Mirror reported.
Poor air quality could be felt in the UK as soon as Wednesday, BBC Weather presenter Carol Kirkwood said.
She said: "There has been very poor air quality today in parts of Spain, and it could well affect us in the southeast and East Anglia on Wednesday."
People in Spain were advised not to stay outside for long periods, said the Laboratorio de Climatologia at the University of Alicante, which recommended mask use.
In some parts, locals were told to avoid exercising altogether.
The air change has also affected the Canary Islands and the Balearic Islands.
Previously, Dr Andy Whittamore - the clinical lead at Asthma UK - warned of the risks posed by Saharan dust.
"Toxic air can leave people struggling for breath and can cause wheezing, coughing, shortness of breath and even a life-threatening asthma attack," he said.
"Saharan dust could pose a serious risk to the 5.4 million people in the UK with asthma.
"Dust and other types of air pollution are a well-known trigger for people with asthma.
"People with asthma must make sure they carry their reliever inhaler (usually blue) with them at all times in case their symptoms worsen.
"We also advise people with asthma to continue to manage their condition with their preventer inhaler (usually brown) as this will help to reduce the inflammation in their airways and make them less likely to react to asthma triggers."
Calima is the Spanish word used to describe when there's sand or dust in suspension in the atmosphere.
There are two types of this phenomenon.
Type A calima refers to natural haze from sand, dust and other particles that come from the environment, whereas type B calima refers to the haze that comes as a result of pollution or ash from a forest fire for example.
Some of Spain's larger cities struggle with poor air quality as a result of pollution, but the most striking episodes of calima come as a result of huge sand clouds from the Sahara blowing over to the Spanish territory - given Spain's relative proximity with the 9.2 million square kilometre desert.
Calima episodes tend to last between three and five days.
A cloud of dust has also covered parts of Switzerland, giving it an unusual yellow glow, with the normally blue sky taking on an orange-brown hue.
Extraordinary images have been shared on social media showing this strange phenomenon in the Swiss Alps.
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