Johannesburg — Former President Nelson Mandela was admitted to hospital for a scheduled medical check-up on Saturday afternoon, the presidency said.
"Doctors are conducting tests and have thus far indicated that there is no reason for any alarm," said spokesman Mac Maharaj.
He said the check-up was to manage existing conditions that came at his age.
Speaking to E News Channel Africa (ENCA), Maharaj said the last time he saw Mandela, he was in great shape.
"He was on that day [in] exceptional shape... he is 94 -- we have to bear that in mind -- and frail."
He said it was not yet known how long the former president would be in hospital.
The presidency would update the public with any information coming from Mandela's doctors.
"They refuse to divulge anything in advance to us," Maharaj said.
"They want the space to be able to do their work and investigations and they do not want us to become alarmed over any issue."
In December last year, Mandela underwent an operation to remove gallstones and to treat a recurring lung infection.
He was discharged after an 18-day stay and was placed under home-based high care at his Houghton home in Johannesburg.
In January, the presidency said Mandela had made a full recovery from the surgery and continued to improve.
South Africa's first black president has a long history of lung problems, dating back to the time when he was an apartheid political prisoner on Robben Island.
While in jail he contracted tuberculosis.
In January 2011 he was hospitalised for two nights for an acute respiratory infection.