The condition of former South African leader Nelson Mandela has deteriorated in recent 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.