The South African presidency said on Thursday the condition of Nelson Mandela has deteriorated in the past two days, but has given no further details.
President Jacob Zuma has cancelled a trip to Mozambique after visiting the 94-year-old who remains critically ill and on life support in a Pretoria hospital. Mr Zuma's spokesman Mac Maharaj said his condition had deteriorated "in the past 48 hours".
Emotional crowds continue to gather outside the hospital, adding messages of support for Mr Mandela and the BBC reports that South Africans now seem resigned to the prospect of his death.
The country's first black president has been in hospital since 8 June with a recurring lung infection and it his fourth admission to hospital in six months.
In the 1980s he was diagnosed with tuberculosis in the 1980s while he was a prisoner on Robben Island and after his release said it was probably caused by the dampness in his cell.
Mr Mandela's health is not improving, but his granddaughter Ndileka Mandela said on Thursday he remained "stable" and the family was taking comfort from messages of support.
A presidential statement said Mr Zuma was briefed by doctors who said they were doing everything possible to ensure Mr Mandela's well-being. Mr Zuma "reiterated his gratitude on behalf of government to all South Africans who continue to support the Madiba family".
Mr Mandela, known by his clan name Madiba, 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 and retired from public life in 2004.
Earlier on Wednesday, Mr Zuma said Mr Mandela's 95th birthday on 18 July would be celebrated with "vigour as it is a life spent in dedication to humanity".