The 94-year-old was taken to hospital in Pretoria overnight aafter his health deteriorated

The former South African President is said to be in a "serious, but stable condition".

A spokesman for the President Mac Maharaj said, "The former president is receiving expert medical care and doctors are doing everything possible to make him better and comfortable." 

"It is a condition he has had over a long period of time ... and we hope this time it will also be treated successfully."

"Some members of his family have been there with him all the time", the South African presidency said in a statement.

It is the second time in recent months Mr Mandela has been in hospital and the fourth health scare in six months for the anti-apartheid leader.

In April of this year Mandela was kept in hospital for 10 days after being treated for pneumonia.