"A chemical test unit will be sent to Omsk? It's main task will be to investigate pollution in the region and establish the degree of danger represented by the anomalous snowfall, " the agency quoted an unnamed official from the ministry as saying.

Snow ranging in colour from light yellow to orange and carrying a distinctive "musty" odour was observed yesterday in five districts of Omsk province, which lies in western Siberia and borders Kazakhstan, Itar-Tass said.

"Residents are advised not to use snow for their household or technical needs and to limit walking, either by people or their pets, in this area, " the official said.

The affected area measures about 1,500sq km and is home to over 27,000 people, the ministry said.

Officials have already been gathering snow samples, it added.

The Omsk province is known as a centre of the oil industry and the provincial capital is among Siberia's largest cities.