GOTHENBURG, Sweden, (AFP) - A sandstorm that hit the Sahara desert last week rained down on southern Sweden early this week, covering buildings and streets in a thin layer of ochre-coloured dust, the Swedish Environmental Research Institute said Tuesday.

Strong northerly winds in the African desert around October 11 lifted billions of microscropic sand crystals up into the atmosphere and carried them thousands of kilometers north, the institute said in a statement.

The dusty mass only fell to the ground on Monday when rains in southern and southwestern Sweden dispersed the sand particles, it said. Numerous residents in the region were surprised to find their cars and sidewalks covered in a thin layer of reddish-brown or yellowish dust, with a texture similar to flour, and called authorities seeking an explanation. Tests conducted on rain samples showed traces of the extremely fine sand particles.

Saharan sand in Northern Europe is anything, but uncommon. It is usually brought to us by a tropical continental air mass carrying the fine sand grains from the Sahara, across the Mediterranean, the Alps and eventually the Channel or North Sea into our latitudes. The phenomenon has occurred before and will again, but is very rare, especially in this time of the year. Saharan dust has at least on one occasion demonstrably been deposited in parts of northern Sweden and Finland. On March, 10 1991, Saharan dust turned snow yellow over wide areas. As the general weather pattern is not changing much over the next few days the phenomenon could reoccur in coming days.