CAPE TOWN: South Africa's violent strikes are a wake-up call for the country and signal several social time-bombs waiting to explode, a former World Bank managing director warned Wednesday.

A rash of deadly labour unrest spiralled out of the Marikana platinum mine last year to other mines, killing more than 50 people, and on to the transport and farming sectors.

"The shrinking economic cake alongside the rising tide of higher expectations that freedom would deliver better material conditions has raised the risk profile of my country," said Mamphela Ramphele, a former anti-apartheid activist who held the senior World Bank post from 2000 to 2004.

"The tragedy then of Marikana and protests by agricultural sector workers in the fruit and wine farms of the Western Cape are a wake-up call, alerting South Africans to the many time-bombs waiting to go off."

Ramphele, who is rumoured to be mulling an entry into politics, said the legacy of the country's past had "come home to haunt us".

Over half South Africa's 50 million people live below the poverty line, 19 years after multi-racial elections ended white minority rule.

Most citizens across the world still don't enjoy the benefits of mineral resources, she told the African Mining Indaba conference.

"For the most, mining tax revenues vanish into the black hole that is the central fiscus and end up funding large rural estates for presidents," she said, in an apparent swipe at President Jacob Zuma amid a scandal over a $23 million- (17 million euro-) upgrade at his private rural home.

Failure by post-apartheid governments to invest in education and training to enhance productivity had resulted in a "classical unsustainable economic base", she said.

Ramphele side-stepped a question on her future political ambitions at the conference, which has drawn thousands of delegates.