website design templatesecommerceCelebrations in Juba began at midnight (2100 GMT). A countdown clock in the city centre reached zero and the new national anthem was played on television.
Saturday's independence ceremony is being held at the mausoleum of the late rebel leader John Garang, who died just months after signing the peace deal that ended Africa's longest-running conflict.
The BBC's Will Ross in Juba says people have flocked to the event on a baking hot day - some of them climbing trees to get a view.
There is a heartfelt display of excitement mixed with relief that after many years of feeling oppressed the tie with the north has finally been cut, he says.
The Speaker of the South Sudan Legislative Assembly, James Wani Igga, read out the Proclamation of the Independence.
Our reporter says people in the crowds have been saying it is a moment to celebrate but they are also talking about the many lost relatives who died during the war.