CAPE TOWN - The robust growth in the African middle class was contributing to the continent's economic growth and was acting as a force for democratisation and entrepreneurship, African Development Bank vice-president and chief economist Mthuli Ncube said yesterday.

Prof Ncube was releasing the development bank's report on this growing social class.

Foreign investors and donors needed to work with members of this class to create new partnerships for development and it should be fostered by policy makers, the bank's report called The Middle of the Pyramid: Dynamics of the Middle Class in Africa, said.

It estimates that the size of the middle class - defined as earning between $2-$4 a day and $2-$20 a day - was about 300-million people, or about 30% of the continent's total population of 1-billion and that it contributed about $800bn to Africa's total gross domestic product of $1,6-trillion annually.

The size of the African middle class is still relatively small as a percentage of the total population compared with advanced economies where this figure is about 80%, but trend analyses of the bank indicated that it would catch up by about 2050 as the population moved from rural to urban areas.

The less-affluent section earning $2-$4 a day totalled about 150-million to 180-million people and was more vulnerable to economic shocks, according to Prof Ncube, a former dean of commerce at the University of the Witwatersrand. He conceded that the daily income used to define the middle class was very low, but said this was the reality on the continent.

He said Africa's middle classes had grown robustly by about 18% between 1980 and 2009-10. The middle classes were a source of democratic stability.