An international conference on the spread of deserts is starting in the Senegalese capital, Dakar.

Delegates have come from one-hundred-and-ninety countries and five-hundred environmental organisations.

The United Nations Convention to Combat Desertification and Drought, which has convened the meeting, says it is the biggest environment meeting ever to be held in Africa.

The conference will try to reach a concensus on how to combat the spread of deserts, so affected countries can get international financial backing to fight the problem.

The organisers estimate that the spread of barren land could eventually threaten a billion people world-wide.