- NEW: World leaders hail the vote in Southern Sudan
- Southerners could usher in the world's newest nation
- About 2 million people died from 1983 to 2005 during a war between the two sides
Juba, Sudan (CNN) -- Tens of thousands of people across Southern Sudan went to the polls Sunday in a historic referendum that they say is a vote for freedom.
Many lined up early to cast their ballots on whether the south should declare independence or remain part of a unified Sudan.
If southerners vote for secession -- as is widely expected -- a new nation would emerge in July, unless some obstacle appeared to prevent that.
Mary Dennis arrived at a polling place in Southern Sudan at 4:30 a.m. to secure her spot near the front of the line.
"I had to come early," Dennis 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 this historic day.
"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."
The Southern Sudan population, made up of mainly black Christians and animists, will vote for a period of seven days.
Even police officers, many of whom were recently recruited to secure a safe vote, couldn't hold back the euphoria Sunday.
"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.
"We welcome the start of polling today for the Southern Sudan Referendum," said a joint statement from U.S. Secretary of State Hillary Clinton, Norwegian Foreign Minister Jonas Store and U.K. Foreign Secretary William Hague.
"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, the statement said.
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, some 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 streamed into their homeland by river and land 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.
Southern Sudanese diplomat John Duku said before the voting that unity, or one 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 people in Sudan have to redefine and reconstruct the relations between north and south after the referendum.
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 in a statement Saturday.
Militias under the operation of rebel commander Galwak Gai led an ambush Saturday morning 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 and friction point in the north-south border region.
Wour Mijak, spokesman for the Sudan People's Liberation Movement in Abyei, 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 injured. Skirmishes continued Saturday, he said.
The SPLM is the governing party of the southern region.
But Hamadi al-Dudu, a Misseriya tribal leader, said Misseriya herders were with their grazing cattle in the area of Umbalayil and they were approached by the Southern Sudanese forces in cars with heavy weaponry.
"It was an unprovoked attack. Our people fought back," al-Dudu said.
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.
