People in parts of south Wales woke to find their cars and houses covered in dust which has come all the way from the Sahara Desert.
Dust from Sahara coating a car at Milford Haven in Pembrokeshire
A number of people were concerned it could be hazardous but experts say there is nothing to be worried about.
Incidents have been reported in Milford Haven, Burry Port, Port Talbot, Cardiff and areas of England.
The dust, which has been blow at high altitude from Africa, will have fallen overnight with light rain.
Colin Pook from Thornton near Milford Haven, Pembrokeshire, described finding "thick white dust" on his car and house.
"Initially I thought it had come from the oil refinery," he said.
Pembrokeshire Council said it had received a number of calls.
A spokesman said: "We've had quite a few inquiries about it here at county hall.
"We had it tested this morning and it's very fine dust originating from the Sahara Desert.
"It's not harmful and the advice we have been giving people is to give their cars a good wash."
The Environment Agency Wales said it had received reports from people across south Wales.
A spokesman said some people had contacted them with concerns it could be hazardous but he assured them it was not the case.
"It is from a sand storm in the Sahara on 20 January," he said.
AEA Technology, which monitors air quality on behalf of the Welsh Assembly Government, said the dust had travelled from the Sahara, out into the Atlantic and had been blown to the UK.
Paul Willis of the company said they had monitored high levels of particle pollution over the last 24 hours but the air had now cleared.
He said it was caused by a big high pressure system sitting over central Europe which had coincided with the sand storm.
The last time it had happened was in March 2007 but he said this week south Wales seemed to have been particularly hit.