Sudan votes in Darfur referendum as rebels boycott
Voting started just after 09:00, an AFP correspondent said.
Ethnic minority rebels in Darfur have been battling forces loyal to President Omar al-Bashir, wanted for alleged war crimes in the region over claims his Arab-dominated government was marginalising them.
Rebels have long demanded a single region but say the vote cannot be free and fair due to ongoing unrest.
Heavy fighting in the Marra mountains at the centre of Darfur has forced at least 100 000 people to flee their homes since January, the United Nations says.
Khartoum has insisted the vote go ahead as it was stipulated under a peace agreement signed in Doha in 2011 with several rebel groups.
The ruling National Congress Party backs the five-state system.
The United States has voiced concerns over the vote, saying that "if held under current rules and conditions, a referendum on Darfur cannot be considered a credible expression of the will of the people of Darfur".
Darfur was a single region until 1994, when it was divided into three states, with a further two added in 2012.
Since the conflict erupted in 2003, at least 300,000 people have been killed according to the UN, and there are some 2.5 million people living there who have had to flee their homes.