"The Sharpeville and Langa massacres were a tipping point in that they served to trigger off deep revulsion and disgust, both locally and internationally, against the apartheid government," he said.

The incidents brought the banning of liberation movements such as the Pan-African Congress, which organized the demonstration, and the African National Congress. It also led these groups to abandon non-violence and take up arms.

The demonstrators were protesting laws that required them to carry pass books at all times or risk arrest. Many burned their pass books and offered to be detained. Instead, police, overwhelmed by their numbers, shot into the crowd.

The incident brought international condemnation, the beginning of the regime's diplomatic isolation and annual demonstrations in South Africa that often were violently suppressed.

Six years later, the United Nations proclaimed the Sharpeville anniversary to be the International Day for the Elimination of Racial Discrimination.

After the end of apartheid in 1994, the new government proclaimed the date South Africa's Human Rights Day and made it a national holiday.

Sharpeville, 50 years later, is still poor. Many residents live in shacks without running water or indoor sanitation.

Last month residents burned tires in the streets to protest what is called the lack of service delivery and local politicians whom they accuse of corruption. Such demonstrations have become frequent in a country with one of the widest gaps between rich and poor in the world.