The condition of former South African leader Nelson Mandela has deteriorated in the last few days, presidential spokesman Mac Maharaj has said.
The announcement came as President Jacob Zuma cancelled a trip to Mozambique following consultations with Mr Mandela’s doctors.
Mr Mandela, 94, South Africa’s first black president, has been in hospital since 8 June with a lung infection.
Emotional crowds continue to gather outside the Pretoria hospital.
They have been adding messages of support for Mr Mandela, known by his clan name Madiba.
Correspondents say South Africans now seem resigned to the prospect of his death.
“We don’t like seeing Mandela going through so much pain, he has had a tough time in his life and he’s gone through a lot of struggle. I think this struggle should get over sooner,” Khulile Mlondleni told the BBC.
“We are all going to feel bad when he passes [away], but at the same time we will be celebrating his life. He has done so many great things for this country,” said 25-year-old John Ndlovu, quoted by Reuters news agency.
Mr Maharaj announced Mr Mandela’s deterioration late on Wednesday evening, after consultations with doctors.
“Over the past 48 hours, the condition of former President Madiba has gone down,” he said.
Mr Zuma said he was cancelling his trip to a regional summit in the Mozambican capital Maputo.
The statement from his office said he “reiterated his gratitude on behalf of government, to all South Africans who continue to support the Madiba family”.
The decision will only reinforce the impression that Nelson Mandela’s life is slipping away, the BBC’s Mike Wooldridge reports from Johannesburg.
But later Mr Zuma’s office warned against speculation about Mr Mandela’s health, saying that announcements about his condition would come from the president himself or Mr Maharaj.
Mr Maharaj criticised some media outlets for broadcasting unverified information, as rumours spread on social media sites.
Mr Mandela is revered for leading the fight against white minority rule in South Africa and then preaching reconciliation despite being imprisoned for 27 years.
He was awarded the Nobel Peace Prize in 1993 and was elected president the following year. He left office in 1999 after a single term.
Mr Mandela retired from public life in 2004 and has rarely been seen at official events since.
He has a long history of lung problems, and was diagnosed with tuberculosis in the 1980s while he was a prisoner on Robben Island.
After his release, Mr Mandela said that the tuberculosis was probably caused by dampness in his prison cell.