An emotional Mr Zuma broke the news to the nation during a live press conference that began about 8.45am AEDT.

"Our thoughts and prayers are with the Mandela family," he said.

"To them we owe a debt of gratitude. They have sacrificed much and endured much so that our people could be free.

"Our thoughts are with the millions of people across the world who embraced him.

"This is the moment of our deepest sorrow our nation has lost its greatest son."

Mr Zuma said Mandela would be farewelled at a state funeral and that the nation's flags would fly at half mast until the funeral.

He also called for South Africans to unite and to farewell Mandela in a manner fitting of his legacy.

"Fellow South Africans, Nelson Mandela brought us together and it is together that we will bid him farewell.

"As we gather to pay our last respect, let us conduct ourselves with the dignity and respect that Mandiba personified.

"Be mindful of his wishes and the wishes of his children.

"May his soul rest in place, God Bless South Africa."