The final verdict that will set the mainly Christian, African south on the road to recognition as the world's newest state in July is not expected until next month.
But figures gathered by AFP from state and county referendum officials around the south showed that 2,224,857 votes for separation from the mainly Muslim, Arab north had already been returned by Wednesday evening.
That comfortably exceeded the simple majority of 1.89 million votes needed on the 96-percent turnout of the 3,932,588 registered voters.
In some areas, the vote for partitioning Africa's and the Arab world's largest nation was almost unanimous in a region still ravaged by a devastating 1983-2005 civil war.
In Lakes state, centred on Rumbek town which served as rebel headquarters during the war, 298,216 of the 300,444 votes cast were for independence, more than 99.9 percent.
Just 227 opted to remain united with the north -- less than a tenth of one percent -- with the balance made up by blank or invalid ballots.
Posters urging people to remember the sacrifices of the estimated two million people who died in the war are ubiquitous in the region's towns. "Make sure the martyrs did not die in vain," voters were repeatedly urged in the referendum run-up.
In the busy Konyo-Konyo market area of the southern regional capital Juba, excitement was high at the news that the vote had been reached.
"It is what we have been wanting for so long," said Moses Adut, a former rebel soldier turned motorbike-taxi driver. "The blessed day is arriving soon."
Traders in the chaotic, sprawling market said they had celebrated at the news that Juba had voted overwhelmingly for separation, but were saving their full partying for the expected formal and final announcement in mid-February.
The once sleepy town now poised to become the world's newest national capital returned a 97.5-percent majority for secession, according to the preliminary results.
"We have been told not to jump the gun, to wait until everything is in order before we celebrate," said Malaak Ajok, a building materials trader.
"I am happy inside to know the results, but I can wait a bit longer. After, all we have been waiting for over 50 years for this moment."
Another man had plastered a poster in support of separation onto the wheelbarrow he uses to carry goods.
"It is the results we were expecting, it was not a surprise," said William Taban, a porter.
"But it is good that the results are... true to what the south believes, that we want to say goodbye to the north."
Poll officials and the former rebel southern government have been meticulous about respecting the agreed procedures for collating the results of the week-long vote, which was the centrepiece of the 2005 peace deal that ended the war.
"We are being methodical to make sure all the rules are respected -- and that takes time, of course," said Aleu Garang Aleu, a spokesman for the Southern Sudanese Referendum Bureau, which is running the vote in the south.
Southern leaders had warned against any premature celebration or triumphalism that might undermine hopes of a "velvet divorce" from the north and an end to the five decades of conflict that have blighted Sudan ever since colonial power Britain decided to grant to it independence as a single nation.