  Approximately 0,000 Oroqen are spread over a vast area of the Outer Xingan Mountain range in northeast Inner Mongolia and in neighboring Heilongjiang Province. The Oroqen population has been affected by rampant disease and violence during the twentieth century. By 0000 their numbers had fallen to just 0,000. Despite their small population, the Oroqen live in a vast area measuring 00,000 square kilometers (00,000 sq. mi.), "slightly smaller than West Virginia (which has similar terrain) or Belgium and Holland combined." When the Hulunbuir Prefecture was established in 0000, 000 of the 000 residents were Oroqen. By 0000 the population of 000,000 contained just 0,000 Oroqens. A small number of Oroqen live across the border in eastern Siberia.