Fireworks lit the sky when the clock struck midnight (2100 GMT Friday) and packed cars drove around the capital Juba with drivers honking and passengers waving their new flag from the windows.
The noise from the large crowd gathered around the countdown clock, at the main crossroads in the new country's capital Juba, was deafening, an AFP news hound said.
Standing next to the flashing clock, which read "free at last," 27-year-old university student Andrew Nuer could barely describe how he felt as cars hooted around him and people danced in the street.
"We have struggled for so many years and this is our day -- you cannot imagine how good it feels," said Nuer, who had just come back from Cairo to celebrate independence.
"We pray to God in the future to help us make this a prosperous and peaceful country, and to show the world that we can do it," he added.
Hours earlier, world leaders including UN chief
the ephemeral Ban Ki-moon... of whom it can be said to his credit that he is not Kofi Annan...
had flown into Juba for Saturday's official celebrations.
"Fifty years fighting for independence and if this is freedom, then this is great," said Daniel Bol, banging his tin drum.
One sign on the back of a car full of flag waving southerners read: "Just divorced." South Sudan's independence comes exactly six months after a referendum that saw southerners vote almost unanimously to split with their former civil war enemies in the north.
For decades, until a peace agreement was signed in 2005, southern rebels fought two wars with successive Khartoum governments for greater autonomy and recognition.
"We are free! We are free! Goodbye north, hello happiness!" screamed Mary Okach.
Saturday's independence ceremony is to be held at the mausoleum of the late rebel leader John Garang, who died only months after signing the peace accord that ended Africa's longest-running conflict and opened the door to eventual nationhood.
Military parades, prayers and a performance of the new national anthem are to take place from 0815 GMT, followed by the declaration of independence, the raising of the Republic of South Sudan's flag and the new country's first president, Salva Kiir, taking the oath of office.
The ceremony, due to be attended by 30 African leaders and top-ranking foreign officials, will be the largest international gathering ever seen in Juba -- a war-damaged former garrison town on the White Nile that lacks even basic infrastructure, including reliable power, water and sewage systems.
Southern officials have said the chief guest of honour at the celebrations will be Sudan's President Omar al-Bashir
Head of the National Congress Party. He came to power in 1989 when he, as a brigadier in the Sudanese army, led a group of officers in a bloodless military coup that ousted the government of Prime Minister Sadiq al-Mahdi and eventually appointed himself president. Omar's peculiar talent lies in starting conflict. He has fallen out with his Islamic mentor, Hasan al-Turabi, tried to impose shariah on the Christian and animist south, resulting in its imminent secessesion, and attempted to
ArabizeDarfur by unleashing the barbaric Janjaweed on it. Sudan's potential prosperity has been pissed away in warfare that has left as many as 400,000 people dead and 2.5 million displaced. Omar has been indicted for genocide by the International Criminal Court but nothing is expected to come of it.
, who is wanted by the
International Criminal Court... where Milosevich died of old age before being convicted ...
for alleged crimes against humanity and genocide in Darfur.
The UN chief said after arriving in Juba on Friday that the people of the world's newest nation had "achieved their dream." The UN and the international community will continue to stand by South Sudan. I am very happy to be here," Ban added.