"Today we shall raise the flag of South Sudan to join the nations of the world," said Pagan Amum, the secretary general of the ruling Sudan People's Liberation Movement, speaking at the base of a giant flagpole.
From early morning, thousands started to arrive at the official venue of Saturday's celebrations, singing songs and carrying flags. It will be the largest international gathering ever seen in this war-damaged former garrison town on the White Nile that lacks even basic infrastructure.
Last-minute preparations have been taking place throughout the capital ahead of the historic ceremony, which is due to be attended by 30 African leaders and senior Western officials.
Workers were still fixing the awning above the VIP seating on Saturday morning, and security was tight, with sniffer dogs and heavily armed soldiers on the streets.
"This is the special day," said Joseph Legge. "We cannot wait to see the flags swap -- north down and south up."
South Sudan's independence comes exactly six months after a referendum 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 successive wars with the north, leaving the region in ruins, millions of people dead and a legacy of mutual mistrust.
The independence ceremony is being held at the mausoleum of the late rebel leader John Garang, who died just months after signing the peace accord that ended Africa's longest-running conflict and opened the door to nationhood.
"This is a historic day, a day of justice, a day I am so happy to see. Today we can move on with a new life and forget the suffering and the pain," said Archbishop Daniel Deng Bol, head of the Episcopal Church of Sudan.
Military parades, prayers and a performance of the new national anthem are due 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.
Southern officials have said the chief guest of honour at the celebrations will be Sudanese President Omar al-Bashir, who is wanted by the International Criminal Court on charges of crimes against humanity and genocide in Darfur.
There were Darfuris among those waiting expectantly at Garang's mausoleum. "We are here to welcome our brothers in the south in independence, and give a message to Bashir, that this is what happens when you oppress a people," said Mohammed Jamous.
Around 200 supporters of Darfur rebel leader Abdelwahid Nur held a banner that read: "The new beginning," and "Together we must stop genocide in Darfur, Nuba Mountains."
The Nuba Mountains in South Kordofan state in the north have seen deadly clashes in the run-up to southern independence between northern troops and pro-southern militia.
French Foreign Minister Alain Juppe has already said he will try to avoid an encounter with Bashir at the independence ceremony. But Khartoum was among the first countries to officially recognise the fledgling nation, which needs all the help it can get to overcome the vast challenges of building a stable and prosperous future.
For this, it must strike a cooperative relationship with the Sudanese leader, given the strong ties that continue to bind the two countries, and despite the strain on relations caused by the bloodshed in the Nuba Mountains.
Talks in Addis Ababa aimed at resolving issues still outstanding between north and south, such as the future status of the disputed border district of Abyei, how to manage the country's oil sector and the fate of southerners in the north and northerners in the south, have so far failed to bear fruit.
UN chief Ban Ki-moon, another key guest at the ceremony, on Friday praised the "political courage" of the Sudanese government in accepting southern independence, after meeting Foreign Minister Ali Karti in Khartoum.
"I know secession is painful, emotionally and financially... While the people of north and south Sudan will soon live in different countries, their future will be closely linked," Ban said, before flying to Juba for the celebrations.