Out of an estimated Asian population of 100,000 in 1967, almost half, most of them with British passports, had left the country by 1980. Arabs, who were the dominant group on Zanzibar before the 1964 revolution in spite of forming less than 20% of the population, fled after the event to the mainland or the Middle East. There is some emigration of laborers seeking work in neighboring countries, but Tanzanians who leave the country without authorization are subject to prosecution on return.
During the clove harvest, labor moves from the towns to the clove plantations, from Zanzibar to Pemba, and from the mainland territories to Pemba. As a result of migration from rural areas to the cities, the urban population is estimated to be growing by 6.5% per year. Urban authorities are empowered to return the unemployed to their villages.
In October 1993, around 250,000 Burundi refugees fled to Tanzania to escape from a military coup in Burundi. Most of these refugees returned within three months. Following the genocide in Rwanda, 500,000 Rwandan refugees arrived in April 1994. In 1996, 220,000 Rwandan refugees in Burundi fled to Tanzania to escape from the fighting in northern Burundi; they were allowed to enter based on humanitarian grounds. By December 1995, around 500,000 were repatriated following an agreement between Tanzania, Rwanda, and the UNHCR. In 1995, 18,000 Mozambicans entered Tanzania. Since 1997, 33,000 Zaireans and 59,000 Burundis have entered Tanzania. As of 1999, there were 415,000 refugees in Tanzania, including 285,000 from Burundi, 118,000 from DROC, 7,600 from Rwanda, and 4,200 from Somalia. In 2001, the net migration rate was -1.4 per 1,000 population. The total number of migrants living in Tanzania that year was 893,000. The government viewed the migration levels as satisfactory.