A boy walks past a mural painted outside the house former South African President Nelson Mandela once lived in, in Johannesburg's Alexandra township June 9, 2013.[Photo/Agencies]

In a two-sentence statement, President Jacob Zuma repeated his call for the country to pray for the ailing 94-year-old, who became the first black leader of Africa's biggest economy after historic all-race elections in 1994.

It is Mandela's fourth hospital stay since December and the use of the word "serious" to describe his condition has intensified concerns about the health of a man revered around the world as a symbol of perseverance and reconciliation.

However, among South Africa's 53 million people there is a growing realisation they will one day have to say goodbye to "Madiba", the clan name by which he is affectionately known.

On state radio on Monday morning, the top two news items were a long-running scandal in the national prosecutor's office and a snap of cold weather hitting Johannesburg.

The previous day, the Sunday Times newspaper struck a philosophical tone, with the front-page headline "It's time to let him go".

"The family must release him so that God may have his own way. They must release him spiritually and put their faith in the hands of God," it quoted long-time friend and anti-apartheid freedom fighter Andrew Mlangeni as saying.

"Once the family releases him, the people of South Africa will follow."

History of lung problems

Mandela has a history of lung problems dating back to his time on the wind-swept Robben Island prison camp near Cape Town.

Before his 1990 release he spent nearly three decades in prison for conspiring to overthrow the apartheid government.

He stepped down as president in 1999 after one term in office and has been removed from politics for a decade. His last appearance in public was at the final of the soccer World Cup in Johannesburg in 2010.

He spent nearly three weeks in hospital in December with a lung infection and after surgery to remove gallstones.

A phalanx of international and local media assembled in front of the Mediclinic Heart Hospital in the capital Pretoria, where Mandela was believed to be staying.

His wife, Graca Machel, had accompanied him to the hospital on Saturday after cancelling a speaking engagement in London, the South African Press Association reported.