The number of people in South Africa who consider themselves religious has dropped by 19 percent, an international survey revealed on Friday.

According to the latest polls released by the Win-Gallup International Religiosity and Atheism Index, which measures global self-perceptions on belief, religious South Africans dropped from 83 percent in 2005 to 64 percent in 2012.

The survey, conducted during November 2011 and January 2012, was based on interviews with 52 000 men and women from 57 countries in five continents.

South Africa was fifth behind Vietnam which dropped by 23 percent, Ireland, 22 percent, Switzerland, 21 percent, and France 21 percent.

According to the survey, 28 percent of South Africans do not consider themselves religious, four percent were convinced atheists, and five percent did not respond to questions.

The survey also indicated that globally the number of people claiming to be religious dropped by nine percent, while atheism rose by three percent.

Ghana was the most religious country in the world with 96 percent, followed by Nigeria with 93 percent.

China had 47 percent of citizens claiming to be atheists, followed by Japan with 31 percent and the Czech Republic with 30 percent.

The survey further indicated that world-wide people in the bottom income groups were 17 percent more religious than those in the top income groups.

The low income group accounted for 66 percent of religious people and the high income groups accounted for 49 percent.