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Nelson Mandela gives an animated speech to the crowd during the South African democracy concert at Trafalgar Square in London in this April 29, 2001 file photo. [Photo/Agencies]

South Africa's President Jacob Zuma visited Mandela at a Pretoria hospital on Sunday, and the medical team informed him that Mandela's condition had become critical over the past 24 hours, according to Zuma's spokesperson Mac Maharaj.

"The doctors are doing everything possible to get his condition to improve and are ensuring that he is well looked after and is comfortable," Zuma said."He is in good hands," added Zuma, appealing to the South Africans and the world to pray for Mandela.

Mandela was admitted to hospital in Pretoria with the serious lung infection on June 8. On March 27, he was hospitalized after doctors diagnosed him of having pneumonia. He was also admitted in December for recurring lung infection.

Mandela suffered from tuberculosis when he was incarcerated for 27 years before the apartheid ended in 1994.

He was the first democratically-elected president in South Africa, having an honor of the state father in the country.