The South Africa government on Monday said that Nelson Mandela's condition remained serious but stable as he continued to receive hospital treatment for a lung infection.

"Former President Nelson Mandela remains in hospital, and his condition is unchanged," the presidency said in a brief statement.

The increasingly frail 94-year-old anti-apartheid leader was admitted to a Pretoria hospital in the early hours of Saturday.

Updates about his health have been infrequent, and the latest tersely worded report is only likely to fuel concerns about the fate of a man who is regarded as the father of modern South Africa.

"President Jacob Zuma reiterates his call for South Africa to pray for Madiba and the family during this time," the government said.

It is the fourth hospital stay since December for the Nobel peace prize laureate, who turns 95 next month.

Although Mandela has long since left the political stage and has not been seen in public since 2010, he remains a towering symbol in South African public life.