The skies in parts of Spain, Germany and Switzerland have turned orange after dust from the Sahara was carried away by Storm Celia.
Brits have been warned the dust could arrive in the UK next.
The orange glow was first spotted in southern areas of Spain on Monday (March 14), with Madrid and Murcia among the places lit up.
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Spanish officials issued extremely poor air quality ratings for Madrid and a large swathe of the country.
The air change has also affected the Canary Islands and the Balearic Islands.
Spain’s national air quality index qualified the capital and large parts of the south-east coast as “extremely unfavourable” – its worst rating.
Spain’s weather service described the dust storm from the Sahara as “extraordinary and very intense”, while adding that it was unclear if it was the worst episode of its kind on record.
Many Spaniards awoke this morning to find a layer of red dust covering terraces, streets and cars.
The sky in the capital and other cities had a gritty tinge to it, while visibility in Madrid and cities like Granada and Leon was reduced to 2.5 miles, the weather service said.
Laboratorio de Climatologia at the University of Alicante warned people against staying outside for long periods.
They recommended the use of masks and in some parts of the country, locals were told to avoid exercising altogether.
On Tuesday (March 15), orange skies were also spotted in Switzerland and Germany.
BBC weather presenter Carol Kirkwood said the poor air quality could be felt in Britain as soon as Wednesday (March 16).
"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", she said.
Previously, Dr Andy Whittamore - the clinical lead at Asthma UK - warned of the risks posed by Saharan dust, reports the Mirror.
"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."
