Nelson Mandela, who was admitted to hospital earlier for a recurrent respiratory infection, is breathing on his own, a spokesman for the South African presidency has said.
The 94-year-old former South African president and anti-apartheid hero was admitted to hospital early on Saturday after battling the infection for a few days.
Mac Maharaj, the spokesman for Jacob Zuma, the current president, said it was a positive sign he was breathing on his own.
"What I am told by doctors is that he is breathing on his own and I think that is a positive sign," he said. "Madiba [Mr Mandela's clan name] is a fighter and at his age, as long as he is fighting, he will be fine."
Mr Maharaj earlier said Mr Mandela's health was "serious this time," adding: "Every day that he gets older it gets more serious."
"The problem is that his infection reoccurred," he told The Telegraph. "At 1.30am today the doctors came to the conclusion that his condition had deteriorated enough that it warranted hospital treatment."
Mr Mandela is known to have been on and off a ventilator in recent months but is understood to be breathing on his own this morning.
His wife Graca, flew home from a hunger summit in London to be at his bedside in Pretoria, the nation's capital.
Mr Mandela is due to turn 95 on July 18. He was also expected to receive a visit from President Barack Obama, who is due to visit South Africa at the end of this month.
In a statement, Mr Maharaj said Mr Mandela, with whom he served time on Robben Island in prison for their battle against apartheid, was "receiving expert medical care".
"He remains in a serious but stable condition," the statement said. "Doctors are doing everything possible to make him better and comfortable."
In March Mr Mandela spent 10 days in hospital with the same lung condition, having similarly been taken from his home by ambulance in the early hours. He was last seen in April, looking frail, unsmiling and dazed . The South African government came under criticism for the images, aired by the public broadcaster SABC, showing him sitting upright on a couch, with his legs covered in a blanket.
There, once stablised, he underwent a procedure to drain a build-up of fluid from his lungs, caused by the recurrence of pneumonia.
In December, he spent nearly three weeks including Christmas Day in hospital for the same lung infection, and to undergo non-invasive surgery to remove gallstones.
In April, the ANC was widely condemned when it released footage of a visit by its senior members, including President Zuma, to Mr Mandela at his home in Houghton, Johannesburg. Despite Mr Zuma's assurances that Mr Mandela was well, his dazed and weak appearance in the footage shocked South Africans.
This morning's news prompted the usual flood of wellwishers.
Jackson Mthembu, the ANC's national spokesman, said the party and its supporters were praying for the former president and his family.
"We call upon South Africans and the peoples of the globe to do the same for our beloved statesman and icon, Madiba," he said.
"We send to him our well wishes for a speedy recovery so that he may soon be discharged to return to the care and comfort of his home."
Twitter: David Cameron - My thoughts are with Nelson Mandela, who is in hospital in South Africa
Patrick Craven, spokesman for the country's biggest trade union, Cosatu, also sent its best wishes.
"Our 2.2 million members, thousands of working people, millions of South Africans and countless more freedom-loving people around the world are thinking of you today," he said. "Madiba's contribution to the struggle for freedom and democracy has been second to none and he has deservedly become a revolutionary icon and a model of all people battling against tyranny, exploitation and poverty. Long may he continue to inspire us!"
During his last hospital admission, Mr Mandela's oldest grandson told The Telegraph that his family were under no illusions about his state of health.
“We have been blessed as a family to have my grandfather all these years with us, we have cherished every moment and continue to do so,” Mandla Mandela said.
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