Sudan's first competitive presidential, legislative and gubernatorial elections in 24 years have already been hit by wide accusations of fraud and procedural mistakes.
The poll, agreed under a 2005 peace deal that ended more than two decades of north-south civil war, was supposed to help bring the oil-producing state back to democracy more than two decades after a military-led coup.
Following a series of boycotts by leading parties over accusations of fraud, the ballot now looks likely to confirm incumbent President Omar Al-Bashir.
Officials from Sudan's National Elections Commission told Reuters they were considering suspending voting for seats in national and state assemblies in some states after discovering they had printed the wrong party symbols next to some candidates' names on ballot papers.
"Logos have been swapped in a very limited number of constituencies," said commission Deputy Chairman Abdullah Ahmed Abdullah.
"According to the law it (the commission) can cancel elections and hold them again within 60 days. That is one of the options we are considering."
Other commission members and international observers told Reuters the printing errors were thought to have affected ballots in 15 to 18 state and national constituencies.
Voting has been taking place in 270 national constituencies and just under 700 state constituencies in African's largest state.
"There are ballots that are missing symbols, duplicate symbols, even missing candidates on some forms, so that (a partial re-run) would be the logical step to take," said one international source close to the elections.
Voting began on Sunday and was extended to last five days to allow more time for voters and officials to deal with the elections' complexities.
Election monitors across Sudan said early voting had been affected by missing ballot boxes, poor staff training and confusion over the location of voting centers.
