Former South African president Nelson Mandela has spent a third day in hospital, with the government saying he continues to be "serious but stable".

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

Mandela was taken to a hospital on Saturday with a lung infection. It was his fourth hospitalisation since December.

A statement issued for the Desmond and Leah Tutu Legacy Foundation described Mandela as "the beloved father of our nation" and offered prayers for a man seen by many around the world as a symbol of reconciliation because of his peacemaking role when white racist rule ended in South Africa.

Mandela "once again endures the ravages of time in hospital," said the Cape Town-based foundation, which was founded by retired archbishop Tutu and his wife Leah to promote peace. "We offer our thanks to God for the extraordinary gift of Mr Mandela, and wish his family strength."

In its brief statement on Mandela's health, the presidency said Jacob Zuma "reiterates his call for South Africa to pray for Madiba and the family during this time," referring to Mandela by his clan name.

During a hospital stay that ended April 6, doctors diagnosed him with pneumonia and drained fluid from his chest.

Mandela has been particularly vulnerable to respiratory problems since contracting tuberculosis during 27 years as the prisoner of the white racist government.

The bulk of that period was spent on Robben Island, off the coast of Cape Town where Mandela and other prisoners spent part of the time toiling in a stone quarry.

He was freed in 1990, and then embarked on peacemaking efforts during the tense transition that saw the demise of the apartheid system and his own election as president in 1994.

Source: Agencies