(CNN) -- Former South African President Nelson Mandela is now in critical condition in a hospital in Pretoria, the president's office said.
Mandela's condition worsened in the past 24 hours.
"The doctors are doing everything possible to get his condition to improve and are ensuring that Madiba is well-looked after and is comfortable. He is in good hands," President Jacob Zuma said in a written statement, referring to Mandela's tribal name.
Mandela has been hospitalized in Pretoria since June 8 for a recurring lung infection. Previously, authorities had described his condition as serious but stable.
Mandela, 94, has become increasingly frail over the years and has not appeared in public since South Africa hosted the World Cup in 2010.
The anti-apartheid hero has been in and out of the hospital in recent years.
His history of lung problems dates to when he was a political prisoner on Robben Island during the apartheid era, and he has battled respiratory infections.