President Jacob Zuma has sought to reassure South Africans as Nelson Mandela is being treated for the recurrence of a lung infection.In an interview with the BBC, Mr Zuma said that people "must not panic" and that the former president was doing "very well" so far.The 94-year-old was admitted to hospital before midnight on Wednesday.He spent 18 days in hospital in December undergoing treatment for a lung infection and gallstones.In a statement released earlier, Mr Zuma's office said the ex-leader was "responding positively" to treatment.The presidency has not identified the hospital where Mr Mandela is being treated.Speaking to the BBC's Lerato Mbele, Mr Zuma said people should "slow down the anxiety"."Of course I have been saying to people, you should bear in mind Madiba is no longer that young and if he goes for check-ups every now and again, I don't think people must be alarmed about it. I would like to really say the country must not panic," Mr Zuma said.The former president is often fondly referred to by his clan name, Madiba.When asked if people should prepare for the inevitable, Mr Zuma said: "In Zulu, when someone passes away who is very old, people say he or she has gone home. I think those are some of the things we should be thinking about."But he stressed that Mr Mandela had been able to handle the situation "very well" so far."Very few outstanding personalities in the world live to his level," he said.Mr Zuma said he was in touch with doctors about visiting Mr Mandela in hospital as soon as possible.Mr Mandela is regarded by many South Africans as the father of the nation for leading the struggle against apartheid.He served as South Africa's first black president from 1994 to 1999.It is the fourth time, Mr Mandela has been admitted to hospital in just over two years.He first contracted tuberculosis in the 1980s while detained on the windswept Robben Island where he served 18 of the 27 years he was imprisoned for sabotage.His lungs are said to have been damaged when he worked in a prison quarry.Despite his long imprisonment, Mr Mandela forgave his former enemies and as president urged South Africans of all races to work together and seek reconciliation.In 1993 he was awarded the Nobel Peace Prize.The treatment Mr Mandela received in December 2012 was his longest spell in hospital since leaving prison in 1990.Earlier this month he spent a night in hospital following a check-up.Mr Mandela retired from public life in 2004 and has been rarely seen in public since.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.