KHARTOUM, Sudan -- Only a trickle of voters, some in uniform, showed up at a polling station in Sudan on Monday as the country took part in an election that will almost certainly extend the 25-year rule of President Omar al-Bashir, the world's only sitting head of state wanted on genocide charges.

As polls closed at 6:00 p.m. (1500 GMT) on the first of three days of voting, election employees counted ballots. In one middle class neighbourhood, just 3 per cent of more than 3,000 registered voters had turned up.

"This is extremely low," an election employee said as he locked up the centre. "I don't know what is going on. We didn't expect that." He spoke on condition of anonymity because he was not authorized to speak to the press.

The second multi-candidate election to be held in Sudan since al-Bashir came to power in a bloodless 1989 coup has been boycotted by major opposition parties. They had demanded postponement until the formation of a coalition government to oversee the vote and ensure its fairness.

The opposition also campaigned for ending al-Bashir's rule, spray-painting "irhal" or "leave" on walls and election posters. But they said widespread voter apathy, and not their boycott, would be the main cause of the expected low turnout.

The election has generated little excitement in Sudan, but is not entirely insignificant. Al-Bashir must remain in office to ensure he is never sent to the Hague to face war crimes charges related to the Darfur conflict, and needs at least the veneer of legitimacy to attract badly needed foreign aid and investment after the 2011 secession of oil-rich South Sudan.

Al-Bashir arrived at a polling centre to cast his ballot dressed in white traditional robes, surrounded by bodyguards and top state officials. The 71-year-old leader waved to his supporters and said "God is great" before leaving in a convoy.

Al-Bashir's polling centre, at a school in central Khartoum, is surrounded by buildings belonging to the security establishment. Residents said plainclothes intelligence personnel flocked to the centre to cast their ballots, as did men in uniform.

Al-Bashir has ruled Sudan unchallenged for 25 years and presents himself as a guarantor of stability. He survived the 2011 Arab Spring and his massive security apparatus has left the once-vibrant opposition a husk of its former self.

In the impoverished Khartoum district of al-Ezba, a handful of female voters sat on benches waiting for their turn as they complained about the lack of electricity, clean water, hospitals, schools and health insurance.

"The people love al-Bashir and I hope he can do something to fix things," said Um Zain, mother of four children.

The 2011 secession of South Sudan, which ended Africa's longest-running civil war, deprived Khartoum of a third of its territory and population, and nearly 80 per cent of its oil revenues. At least three major insurgencies are raging in the country's east, west and south.

Economic losses from South Sudan's succession forced al-Bashir to embark on austerity measures in 2013 that sparked the largest anti-government demonstrations of his rule. Security forces clamped down, killing some 200 people and arresting hundreds more.

Al-Bashir has nevertheless clung to power, which virtually ensures he will never have to face ICC charges of genocide and crimes against humanity related to Darfur, where 300,000 people were killed and 2 million were displaced during a the government's brutal response to an armed rebellion.

"Al-Bashir is wanted," said top opposition figure Amin Mekki, who was released after four months in detention for signing a joint opposition initiative demanding a delay of the vote. "The presidency is the only way to remain immune."

Nearly 13 million people are registered to vote for president and the 450-member legislative council. Some 11,000 polling centres will be open through Wednesday, and results are expected on April 27.

Many expect a repeat of the vote-rigging that took place during the first multi-candidate election in 2010, when al-Bashir won with 68 per cent.

Ibrahim Ghandour, a top presidential aide, dismissed the allegations, saying the government has taken all measures to ensure fair and free elections.

"You have seen it all ... we will have night guards for ballot boxes, unless you are talking about ghosts we don't see," he said.

Ghandour confirmed that at least seven constituencies in restive South Kordofan were unable to vote after rebels seized ballot boxes.

Rebels are battling government forces in South Kordofan, Blue Nile and Darfur, fighting that has displaced tens of thousands of people in recent years.

There were no major protests on the first day of the voting, but activists said more than 20 dissidents disappeared or were unlawfully detained in the three days ahead of the vote.

Activist Sandra Farouk was snatched from her car after delivering a speech at a gathering of the Umma Party, a leading opposition group, on Sunday, according to Galal Youssef, a political detainees' co-ordinator.

Mohammed Hashim, a businessman who voted Monday, defended the crackdown, saying "detentions are meant to preserve the rights of others."

"The Arab Spring produced wars and failed to embody people's dreams," he said. "The Arab Spring failed and what we have here is better."