Ailing former South African leader Nelson Mandela has been placed on life support as he battles to stay alive long enough to enjoy a visit from U.S. President Barack Obama.

The humanitarian hero has been in a critical condition in a Pretoria hospital for days and on Wednesday (26Jun13), his condition took another turn for the worse, according to government officials.

Mandela, 94, was hospitalised on 8 June (13) for a recurring lung infection. His family members and longtime medics are keeping a bedside vigil while fans outside the hospital await news of his condition.

Reports also suggest Archbishop Thabo Makgoba stopped by the hospital on Wednesday, and conducted prayers calling for "a quiet night and a peaceful, perfect end" for Mandela.

President Obama and his wife Michelle are scheduled to arrive in Africa on Wednesday, stopping in Senegal before heading to South Africa to visit the former leader on Friday (28Jun13).