Juba, Sudan (CNN) -- Polling stations across Southern Sudan began counting Saturday ballots cast in a weeklong referendum whose result could split the country into two.
Voting ended at 6 p.m. Saturday and officials -- monitored by local and international observers -- began the long process of counting the millions of votes cast since January 9.
Nearly 4 million people were registered to vote in the referendum that will determine whether Southern Sudan should declare independence from a government based in the north. Thousands traveled by ferry or bus, some traveling for days just to participate in the historic referendum.
As the final minutes ticked down to the closing of the polls Saturday evening, a local band and church choir in Juba could be heard singing, celebrating and urging last-minute voters to cast their ballots. One song included the lyrics, "Bye, bye Khartoum," the capital of Sudan located in the northern region.
Southern Sudanese in the diaspora also cast ballots in the United States and seven other countries.
Officials in Southern Sudan said preliminary results show more than 60% of registered voters had cast ballots in the independence referendum, crossing the threshold needed for it to be valid. Officials speculated that final turnout numbers could be as high as 91%.
As of Friday evening, about 3.1 million out of 3.7 million registered voters in Southern Sudan had cast their ballots, representing a turnout of about 83%, according to Mohamed Ibrahim Khalil of the Southern Sudan Referendum Commission. Outside the country, 55,000 of 60,000 people voted, and in northern Sudan, 62,000 people voted out of 116,857 registered voters.
Khalil described the process as orderly, peaceful and civilized.
"I have not encountered a single Southern Sudanese who is interested in voting for unity. I would say at least 98% of them will vote for separation," said Ezekiel Lol Gatkuoth, who leads the Southern Sudan's mission in the United States.
"This is what we have been fighting for for more than 50 years."
At one polling station in Juba, 95 of the first 100 votes tallied were for secession and five were in favor of unity, according to a CNN count.
An electrical line was run through the polling center so officials could count overnight with help from a light bulb.
Preliminary results are expected to be announced January 31, Khalil said.
U.N. Secretary-General Ban Ki-moon commended the work of the referendum commission, his office said in a statement Saturday.
"The Secretary-General congratulates all the people of Sudan for the display of wisdom, patience, and peaceful determination that has characterized the voting over the last week. He calls on the people and institutions of Sudan to exercise patience and restraint until the Southern Sudan Referendum Commission announces the final result of the referendum."
The referendum is part of a 2005 peace agreement that helped end two decades of civil war that killed about 2 million. The war pitted a government dominated by Arab Muslims in northern Sudan against black Christians and animists in the south.
About 80% of Sudan's oil reserves are in the south, another flashpoint in the war.
The conflict scarred an entire generation in remote Southern Sudan, which is the size of Texas but only has 30 miles of paved roads.
Southerners -- and their ancestors -- have long felt dominated by the north.
"We have waited for 50 years, and we want to be separate," said John Baptiste, a voter.
Sudanese President Omar al-Bashir, wanted for war crimes after mass killings and rape in the country's western Darfur region, has said that a southern vote for independence would be like "cutting off a part of the nation's body but not the end of the world."
Al-Bashir has said he will honor the results, though analysts are concerned he might not keep his word.
"We will greet the result with forgiveness, and patience, and acceptance and an open heart, God willing," he said.
Election officials have said early results will start trickling in Sunday.
The south would become a new nation in July if voters choose independence and no other obstacles emerge.
CNN's Ingrid Formanek and David McKenzie contributed to this report.