President Jacob Zuma's spokesman Mac Maharaj said the Nobel laureate was being treated for a condition "which is consistent with his age". He said there was no cause for alarm. "The medical team is assured of our support as they look after and ensure the comfort of our beloved founding President of a free and democratic South Africa."

A person close to the Mandela family said: "He has not been talking ... he is not looking good. It's clear that something is troubling him."

Mandela's former wife, Winnie Madikizela-Mandela and her daughter Zindzi went ahead with their attendance at the Soweto derby between Orlando Pirates and Kaizer Chiefs.

The Sunday Times has established that the presidency was asked on Friday to fly Mandela's doctors down to the Eastern Cape.

Deputy President Kgalema Motlanthe cancelled a visit to Mandela on Friday after being told of his condition. He had been scheduled to visit Mandela at his Qunu home and address a meeting of ANC members in Mthatha on Friday.

Motlanthe's office would not say why the meeting had been called off. Motlanthe's spokesman, Thabo Masebe, said: "All I know is that there was a planned visit to Mandela, but the deputy president decided to cancel and attend to state matters."

Motlanthe is acting president while Zuma is in Tanzania for a meeting of the Southern Africa Development Community.

Mandela was taken to hospital as his family prepared for the home-coming ceremony on December 15 of Zindzi's youngest son, Bambatha, 23, who had undergone circumcision in Qunu.

Last Sunday several villagers from Qunu told the Sunday Times that they had not seen Madiba in a while.

Concerns over Mandela's health escalated on Wednesday when a SA Defence Force aircraft vanished en route to Mthatha. At first it was speculated that the aircraft carried medical personnel or medical equipment.

But last night Department of Defence spokesman Siphiwe Dlamini said the aircraft, which crashed killing all 11 on board, "had nothing to do with" Mandela or his health.

"There were no medical personnel on board at all ... and that flight had nothing to do with the old man," he said, adding that the department was responsible for Mandela's medical treatment and transportation of medicine.

Mandela has had few public appearances in recent years - the last major one being during the final 2010 Soccer World Cup, when he was carted around the pitch on a golf cart shortly before kick-off.

Besides several visits from Zuma this year, only three other visits to his home in Qunu were reported:

Former US president Bill Clinton and his daughter Chelsea wished him well on his 94th birthday on July 18;

ANC chairwoman Baleka Mbete in May took the ANC's centenary torch to Mandela to mark the party's 100th anniversary; and

US Secretary of State, Hillary Clinton, had lunch with Mandela and his wife, Graça Machel, in August. Clinton reportedly said of Mandela "That's a beautiful smile!" when taking pictures with him.

In the past two years two health scares had the nation on edge. In January 2011 Mandela was treated at Milpark Hospital in Johannesburg for a respiratory infection.

In February this year, he was admitted for "routine tests". It later emerged he had undergone a small procedure to establish what caused abdominal pain.

Mandela has enjoyed remarkable health but has had a few problems in his 93 years.

In 1985 he underwent surgery for an enlarged prostate gland and in 1988, while serving his life sentence, Mandela was diagnosed with early-stage tuberculosis. In 1994, aged 75, he had cataract surgery a few months after being sworn in as President. Press photographers were asked not to use a flash when taking pictures of him. His tear glands had been damaged by years of smashing limestone rocks in the quarry on Robben Island. In 2001 Mandela received radiotherapy for prostate cancer. He told reporters the following year that he had been given a clean bill of health.