Former South African President Nelson Mandela has made steady progress and is "in good spirits" after spending a second night in hospital under treatment for a lung infection.

The 94-year-old is undergoing his third hospital treatment in four months.

"The presidency wishes to advise that former President Nelson Mandela is in good spirits and enjoyed a full breakfast this morning," President Jacob Zuma's office said in a statement.

"The doctors report that he is making steady progress. He remains under treatment and observation in hospital," the statement added.

Mr Zuma's government had said previously Mr Mandela was responding well to treatment after he was admitted to hospital before midnight on Wednesday.

Global leaders have sent best wishes for the Nobel Peace Prize laureate.

Mr Mandela became South Africa's first black president after winning the country's first all-race election in 1994.

A former lawyer, he is revered at home and abroad for leading the struggle against white minority rule, including spending 27 years in prison on Robben Island, and then promoting the cause of racial reconciliation.