"Former President Nelson Mandela has today, 8 December 2012, been admitted in hospital in Pretoria to undergo tests," Zuma's office announced. Mandela "is doing well and there is no cause for alarm," it added.

The ageing statesman, who turned 94 in July, has grown frail and has not appeared in public since South Africa's Football World Cup final in 2010.

Rumours of his failing health flare up periodically, forcing the government to issue reassurances that all is well.

His last hospitalisation was in February when he spent a night in hospital for a minor exploratory procedure to investigate persistent abdominal pain.

"Mandela will receive medical attention from time to time which is consistent with his age," said Zuma's office in a statement.

Mandela spent 27 years in prison for his fight against white minority rule under apartheid, becoming the country's first black president in 1994 at the end of white minority rule.