After 50 years of devastating conflict, south Sudanese finally get a vote on Sunday on whether to remain part of Africa's largest nation or break away as the world's 193rd state.
Polls will open at 0500 GMT and close at 1400 GMT for the first of seven days of voting in a historic referendum that is the centrepiece of a 2005 north-south peace deal that ended Africa's longest running conflict.
Euphoria gripped the regional capital, Juba, on the eve of the launch of polling as people feted the looming end of a long and often difficult countdown. Hollywood star George Clooney joined a host of current and former world statesmen, including senior US Senator John Kerry, former president Jimmy Carter and ex UN chief Kofi Annan, in the city for south Sudan's big day.
But the celebrations were overshadowed by deadly clashes with armed tribesmen and renegade militiamen in two remote oil producing districts on the north south border.
South Sudanese president, Salva Kiir told his people that there was no alternative to peaceful coexistence with the north.
"Fellow compatriots, we are left only with a few hours to make the most vital and extremely important decision of our lifetime," he said. "Today there is no return to war. There is no substitute for peaceful coexistence".
"The referendum is not the end of the journey but rather the beginning of a new one," he added, alluding to the six month transitional period to recognition as an independent state stipulated by the 2005 peace agreement.
US envoys had led an intensive international diplomatic effort right up to the last minute to ensure that the referendum went ahead as scheduled under the deal. Washington's Sudan envoy, Scott Gration alone made 24 trips to the region.
Aides say President Barack Obama, grounded in a commitment to Africa, from where he traces part of his lineage, left administration officials in no doubt of the grave stakes posed by Sudan's potential split.
"'Let me be clear about what this means to me,'" one official quoted Obama as saying during a staff meeting earlier this year. "'Two million people died the last time there was a conflict between north and south. That cannot happen again.'"
The conflict between the Arab, mainly Muslim north and the African, mainly Christian south, has blighted Sudan virtually since independence from Britain in 1956, and further fuelled by ethnicity, ideology and resources, particularly oil.
President Omar al-Bashir, an army man who led the north's war effort against the south for a decade and a half before signing the 2005 peace deal, has said he will respect the outcome of the vote if it is "free and transparent."
On Thursday, the UN Security Council said its members "appreciate" that stance, in a rare act of praise for a man who is wanted by the International Criminal Court for war crimes, crimes against humanity and genocide over his government's handling of the seven year old rebellion in Darfur.
The outcome of the referendum will be decided by a simple majority, but the peace deal stipulates that 60% of the nearly four million voters must turn out for the result to be valid. Ballot papers carry symbols as well as the referendum question in both English and Arabic -- an estimated 80% adults cannot read or write after entire generations missed out on an education during the civil war.
If south Sudan does become independent, it will rank as one of the poorest nations in the world and remain heavily dependent on international aid.