Juba, Sudan (CNN) -- Tens of thousands of people across Southern Sudan went to the polls Sunday in a historic referendum that an international election observer said appeared to have been well-handled.
"There were very, very large numbers from the early hours of this morning all day long," said David Carroll, director of the Democracy Program at the Carter Center, in a telephone interview from Juba. "They were waiting patiently, they were in a happy, celebratory mood. They went through the process in an orderly way, largely. We saw a very meaningful, important process that the southern Sudanese are engaging in with a lot of passion."
By the time polls opened at 8 a.m., many Sudanese had already been standing on line for hours to cast their ballots on whether the south should declare independence or remain part of a unified Sudan.
Those who were still on line at 5 p.m. were allowed to remain there until they were able to vote, he said. "It's something that is clearly very, very important to the people of Southern Sudan."
The Atlanta-based Carter Center has about 70 observers in Sudan and 30 observers in eight other countries where Southern Sudanese are living and voting, Carroll said.
More important than the voting, he said, is what it represents. "This is really moving Sudan into an entirely new future, and it's meaning that the Sudanese are ready to move into a new era."
Also observing the election are representatives of the European Union, the African Union, the Arab League and the Intergovernmental Authority on Development.
If southerners vote for secession -- as is widely expected -- a new nation would emerge in July, unless some obstacle were emerge to prevent that.
Mary Dennis arrived at a polling place at 4:30 a.m. to secure her spot near the front of the line. "I had to come early," she said. "This is a vote for our country."
Edwina Loria, 18, was determined to cast her ballot. "I want to be a first-class citizen," she said, "I want independence."
John Baptiste and his friend showed up before 4 a.m. They sat on the ground with a radio to monitor news of the day's events.
"I am on a mission," Baptiste said. "My mission is to vote. We have waited for 50 years, and we want to be separate. We have planned for many days to be here first."
Voting by the southern Sudan population, made up mainly of black Christians and animists, is scheduled to take place over seven days.
Even police officers, many of whom were recently recruited to secure a safe vote, shared Sunday in the enthusiasm.
"This is such a big day for us, it is the first time we have hope for south Sudan," Ajak Awach Deng said in his new camouflage uniform. "We want freedom, we want our new country and to build our nation."
World leaders hailed the vote.
"Not every generation is given the chance to turn the page on the past and write a new chapter in history," wrote U.S. President Barack Obama in an op-ed that appeared in Sunday editions of The New York Times. "Yet today -- after 50 years of civil wars that have killed two million people and turned millions more into refugees -- this is the opportunity before the people of southern Sudan."
Obama noted that preparations for the referendum had been behind schedule for much of last year, prompting concerns that it might be delayed.
"It is for this reason that I gathered with leaders from Sudan and around the world in September to make it clear that the international community was united in its belief that this referendum had to take place and that the will of the people of southern Sudan had to be respected, regardless of the outcome.
"In an important step forward, leaders from both northern and southern Sudan -- backed by more than 40 nations and international organizations -- agreed to work together to ensure that the voting would be timely, peaceful, free and credible and would reflect the will of the Sudanese people," he wrote.
U.S. Secretary of State Hillary Clinton, Norwegian Foreign Minister Jonas Store and UK Foreign Secretary William Hague also praised the vote.
"This represents a historic step toward the completion of the Comprehensive Peace Agreement," the 2005 treaty that ended a 22-year north-south civil war that killed about 2 million people and set the stage for the vote, they said in a joint statement.
Western nations played a key role in helping broker the peace deal, as did several East African nations.
But reports of violence on Saturday in the south left many observers and residents concerned about whether the voting period would remain peaceful. Even with a secession vote, stumbling blocks could remain -- about 20% of the border area has not been demarcated, and the division of oil revenues between the two sides could be an issue.
Southern Sudanese people who lived in the north for decades have crossed back into their homeland to vote in the referendum. Meanwhile, some voters in the north said they voted for unity, including one woman who said she didn't see a point in splitting up the country.
But Southern Sudanese diplomat John Duku said, prior to the voting, that an undivided Sudanese nation "means only one thing -- it means war."
"Over the years, unity has imposed war on us, the unity has imposed marginalization on us, the unity has imposed slavery on us," he said. "So, what is the meaning of unity? For the people of south Sudan, it means only war."
Thabo Mbeki, a former South African president and chairman of the African Union High-Level Implementation Panel on Sudan, said the tragic aspect of Sudanese history is that relations between the north and the south "have never been relations of equality," and that's the reason the country endured a long civil war.
He said that, after the referendum, the people of Sudan will have to redefine and reconstruct the relations between north and south.
But deadly skirmishes have erupted recently along the north-south area involving Southern Sudan forces, the latest incidents along the disputed area.
Four rebel soldiers were killed and six captured in an attempted ambush on the forces, the Sudan People's Liberation Army (SPLA) said Saturday in a statement.
Militias under the operation of rebel commander Galwak Gai led an ambush Saturday on SPLA soldiers in the border region's Unity State, but were repelled, according to the army.
The SPLA accused the rebels of trying to disrupt the referendum.
On Friday, the SPLA ambushed and captured 26 rebel troops in Mayom County of Unity State.
There has also been fighting in the Abyei region, a contested border area in the north-south border region.
Wour Mijak, a spokesman for the Sudan People's Liberation Movement in Abyei -- the governing party of the southern region -- said police on Friday intercepted militias of the nomadic Arab tribe, the Misseriya, and skirmishing ensued. One police officer and four members of the militia were killed and six of the militia were wounded. Skirmishes continued Saturday, he said.
But Hamadi al-Dudu, a Misseriya tribal leader, said Misseriya herders were with their grazing cattle in the area of Umbalayil when they were approached by the Southern Sudanese forces in cars with heavy weaponry.
"It was an unprovoked attack," al-Dudu said. "Our people fought back."
The south has repeatedly accused the north of trying to stoke tension by supporting rebels troops to destabilize the south, an allegation the Arab Muslim-led government in Khartoum denies.
The January 2005 Comprehensive Peace Agreement between the Sudanese government and the main rebel group in the south, the SPLM, called for the referendum.
It also envisioned a vote in Abyei, an oil-rich area that the British transferred to northern Sudan in 1905. The agreement says people in Abyei should vote on whether to remain part of the north or return to the south.
Both sides were to have worked out many details by now, but that has not happened, delaying the referendum in Abyei.
CNN's Ben Wedeman in Khartoum, Ingrid Formanek in Juba and Nima Elbagir in Balom contributed to this report.