Johannesburg. Churches across South Africa are holding prayers for Nelson Mandela, who has been in hospital for four days being treated for pneumonia.Several hundred people gathered at the Regina Mundi church in Soweto, once a focal point of the struggle against apartheid.At the weekend, South Africa’s presidency said Mandela, 94, was breathing without difficulty. It said excess fluid had been drained from the lungs to ease his breathing.There are no details yet on how long he will remain in hospital and no statement on his condition has been given for the past 24 hours.After Mandela was admitted to hospital mid-last week, President Jacob Zuma said people "must not panic.”The former president first contracted tuberculosis in the 1980s while detained on windswept Robben Island. His lungs are said to have been damaged while working in a prison quarry. This latest spell in hospital is his fourth in just over two years. Mandela served as South Africa’s first black president from 1994 to 1999 and is regarded as the father of the nation for leading the struggle against apartheid.Pleural effusionThe statement read by presidential spokesman, Mac Maharaj, at the weekend, said Mandela had been admitted to hospital "due to a recurrence of pneumonia.”It said: "Doctors advised that due to the lung infection, former President Mandela had developed a pleural effusion which was tapped. This has resulted in him now being able to breathe without difficulty."He continues to respond to treatment and is comfortable.”Maharaj, a prisoner on Robben Island with Nelson Mandela in the 1960s and 70s, said the presidency "would like to acknowledge and thank all who have been praying for, and sending messages of support for, Madiba and his family.”Madiba is Mandela’s clan name and is widely used to refer to him.The hospital Mandela is attending has not been disclosed.Last December Mandela was treated for a lung infection and gallstones, his longest period in hospital since leaving prison in 1990. In February, he was treated for a stomach condition.In 1993 he was awarded the Nobel Peace Prize.His main home is in Qunu, a small rural village in Eastern Cape province, where he says he spent the happiest days of his childhood.However, doctors said in December he should remain at his home in the Johannesburg neighbourhood of Houghton to be close to medical facilities.Agencies