• The United Nations publishes annual population projections for future years, and we looked at the cities with the biggest projected growth by 2035.
  • Among the fastest-growing cities are three cities located in Tanzania.
  • Visit Business Insider's homepage for more stories .

The world population is expected to grow to 8.6 billion in 2030 , and African metro areas are leading this growth.

According to a 2017 UN press release , population growth will mainly occur in nine countries, including five African countries Tanzania, Congo, Uganda, Nigeria, and Ethiopia. The 15 fastest-growing cities, all located in Africa, are projected to almost double their populations by 2035.

Africa is growing so quickly because of its increasingly large young population, the highest of any continent. Over 75% of its population is younger than 35,according to the United Nations Office on the Special Adviser of Africa .

The United Nations Department of Economic and Social Affairs publishes population estimates using data from national censuses and specialized population surveys. We examined the cities that are projected to most rapidly grow in size over the next 15 years among urban areas that had at least 300,000 residents as of 2018 based on the UN's projections of 2020 and 2035 city populations.

Here are the 15 fastest-growing global cities and their expected change in population:

15. Lilongwe, Malawi, has an estimated 2020 population of 1,122,000 and is projected to grow by 97% to 2,210,000 in 2035.

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Carolyn Kaster/AP

14. Ouagadougou, Burkina Faso, has an estimated 2020 population of 2,780,000 and is projected to grow by 97% to 5,481,000 in 2035.

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Luc Gnago/Reuters

13. Uige, Angola, has an estimated 2020 population of 511,000 and is projected to grow by 98% to 1,013,000 in 2035.

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Florence Panoussian/Getty Images

12. Bobo-Dioulasso, Burkina Faso, has an estimated 2020 population of 972,000 and is projected to grow by 100% to 1,940,000 in 2035.

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Christophe Ena/AP

11. Dar es Salaam, Tanzania, has an estimated 2020 population of 6,702,000 and is projected to grow by 100% to 13,383,000 in 2035.

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Emmanuel Herman/Reuters

10. Tete, Mozambique, has an estimated 2020 population of 371,000 and is projected to grow by 101% to 744,000 in 2035.

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Goran Tomasevic/Reuters

9. Niamey, Niger, has an estimated 2020 population of 1,292,000 and is projected to grow by 101% to 2,600,000 in 2035.

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Joe Penney/Reuters

8. Bunia, Congo, has an estimated 2020 population of 679,000 and is projected to grow by 101% to 1,368,000 in 2035.

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Goran Tomasevic/Reuters

7. Gwagwalada, Nigeria, has an estimated 2020 population of 410,000 and is projected to grow by 102% to 827,000 in 2035.

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Charles Dharapak/AP

6. Mwanza, Tanzania, has an estimated 2020 population of 1,120,000 and is projected to grow by 102% to 2,267,000 in 2035.

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Danita Delmont/Shutterstock

5. Songea, Tanzania, has an estimated 2020 population of 353,000 and is projected to grow by 110% to 740,000 in 2035.

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Songea Municipal Council

4. Kabinda, Congo, has an estimated 2020 population of 466,000 and is projected to grow by 110% to 979,000 in 2035.

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Christine Nesbitt/AP

3. Kampala, Uganda, has an estimated 2020 population of 3,928,000 and is projected to grow by 112% to 7,004,000 in 2035.

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James Akrena/Reuters

2. Zinder, Niger, has an estimated 2020 population of 489,000 and is projected to grow by 118% to 1,065,000 in 2035.

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StreetVJ/Shutterstock

1. Bujumbura, Burundi, has an estimated 2020 population of 1,013,000 and is projected to grow by 123% to 2,263,000 in 2035.

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Christopher Morley-Pegge/Shutterstock

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