Michael Aween and his wife Angelina were the only southerners at a school turned voting centre in north Khartoum shortly after it opened. "It's a historic time for me because I'm voting to decide the future of my country," said Angelina Aween.
"We're coming to vote early because we're leaving Khartoum to go back to our home in Lakes state," her husband added.
Only around 117,000 people are registered to vote in north Sudan, the majority of them in capital, compared with 3.75 million in the south.
Another 60,000 southern Sudanese living abroad are registered to vote in eight different countries.
According to the latest census, in 2008, there were some 500,000 southerners in north Sudan, although the autonomous southern regional government and aid groups have estimated the southern population in the north to be at least 1.5 million.
In recent months, many have returned to the south.
The week-long independence referendum is expected to lead to the partition of Africa's largest nation and the creation of the world's 193rd UN member state.