In 2050, the African continent is expected to have 349 million youth, or 29 percent of the world's total, a sharp rise from the 9 percent of the world's youth in 1950, the report noted.

It also pointed out that HIV prevalence appears to be on the decline in Africa, although the rate of infection is still much higher than elsewhere. Swaziland has the highest rate of HIV infection in the world, with 26 percent of people aged between 15 and 49 being HIV positive.

Although Africa has a seventh of the world's people, it has a quarter of the world's refugees, the report said, adding that global population numbers are on track to reach 7 billion in 2011, just 12 years after reaching 6 billion in 1999.

Virtually all of the population growth is in developing countries, while the growth of the world's youth population is shifting into the poorest of those countries, according to the report.