Asked for further details about Mandela's state, Zuma said: "I'm not a doctor". He added: "When a person is critical, a person is critical. I can't say how critical."
The President said: "He's the man we all love. I think all of us in the country should accept that Madiba is now old ... His health will trouble him. As a country we need to pray for him to do well, for the doctors to do their work so he can come out of hospital."
Zuma said earlier yesterday that Mandela's condition had taken a turn for the worse since Sunday.
Mandela is understood to have become increasingly weak and unresponsive and his family have been told to prepare for the worst. The 94-year-old's wife, Graca Machel, has kept a constant vigil at her husband's bedside at Pretoria's Heart Hospital. Yesterday, she was joined by other members of Mandela's large family including his former wife, Winnie, his daughter Makaziwe and granddaughter Ndileka.
Outside the hospital, a bank of flowers, cards and balloons wishing the former president well has built up.
Zuma said there was "no truth" in an earlier report that Mandela, who will be 95 soon, had suffered a heart attack when he was first admitted to hospital on June 9.
It emerged at the weekend that a military ambulance transporting the Nobel laureate broke down on the motorway between Johannesburg and Pretoria, leaving him and his sizeable medical team waiting 40 minutes for a replacement. Zuma said that "all care" had been taken to ensure his medical condition was "not compromised".
"There were seven doctors in the convoy who were in full control of the situation throughout the period. He had expert medical care."
Mandela is almost universally adored by South Africans of all ages and races for leading the country out of apartheid and bringing the warring factions together ahead of democratic elections in 1994. The news of his deteriorating health was met with deep sadness coupled with a sense of resignation. "South Africa has a heavy heart tonight," wrote one of his countrymen on Twitter.
United States President Barack Obama is due to arrive in South Africa on Saturday. Zuma said last night that Obama's visit will go ahead. "You don't stop a visit because someone is ill."
Mandela's problems
Lungs
While serving his 27-year prison term, Nelson Mandela was diagnosed with early stage tuberculosis in 1988 after being admitted to hospital with a bad cough and weakness and having complained of dampness in his cell.
In January, 2011, Mandela was hospitalised for two nights with an unnamed acute respiratory infection at the age of 92.
In December, 2012, Mandela underwent nearly three weeks of treatment for a recurrent lung infection and surgery to extract gallstones.
He also spent one night in hospital in early March this year for what was described as a scheduled check-up. He was readmitted on March 27 for 10 days of treatment for pneumonia when doctors drained a buildup of fluid from his chest, known as a pleural effusion.
On June 8 he was back in hospital with a renewed lung infection after his condition deteriorated.
Prostate
Mandela had surgery in 1985 for an enlarged prostate gland that had caused a urinary blockage.
In 2001, he received radiotherapy treatment for prostate cancer.
Stomach
In February 2012 he spent the night in hospital after a minor exploratory procedure to investigate persistent abdominal pain.
Eyes
Mandela's tear ducts were damaged by years of being forced to smash limestone rocks in the quarry on Robben Island, due to the alkalinity of the stone. He had cataract surgery aged 75 in 1994, a few months after being sworn in as South Africa's first black President.
- AFP
