Electoral commission workers verify ballots brought from polling stations at the central compilation centre in Kinshasa, Democratic Republic of Congo, on Tuesday.

Kinshasa - Voting in parts of the Democratic Republic of the Congo extended into a third day on Wednesday, after logistical problems prevented many voters from casting their ballots on election day, two days earlier.

Some opposition leaders are already calling the elections a sham.

Four presidential candidates said the elections, which had been set to start and finish on Monday, should be cancelled. The official results are expected on December 6, and analysts are warning that violence could erupt unless all participants in the election agree to respect the final outcome.

The African Union and European Union have urged calm, calling on political forces in the country to only use legal means to challenge the results. The US said it was concerned by “anomalies”.

Vital Kamerhe, a former minister, accused the election commission (CENI) of being biased in favour of incumbent President Joseph Kabila, saying widespread fraud was “deliberately planned”.

“These elections must quite simply be annulled,” Kamerhe wrote in a public letter.

International election observers were critical of CENI for failing to adequately prepare the 63 000 polling stations across the country with enough ink, ballot papers and other essential goods.

Workers at the polling stations were also not properly trained in some cases.

Even late on Tuesday, parts of the capital Kinshasa were without ballot papers. The opposition said this was a sign the election commission was biased.

But foreign observers were hesitant to call for a cancellation of the elections, despite the irregularities, which included the burning down of polling stations and attacks by gunmen, which left at least five people dead.

The UN and several African nations stepped in to help ferry ballot papers across the massive Central African nation of 71 million people using helicopters, as the underdeveloped country lacks a proper road network.

Voters say they found pre-filled ballot papers at many stations. Others were simply unable to find their names on registration lists. There are an estimated 32 million voters in the country.

Some 18 500 candidates are running for the 500 seats in parliament. Ten people are challenging Kabila for the presidency, including his main rival, Etienne Tshisekedi, a 79-year-old who is being touted by his party as a reformist.

Tshisekedi, who has already declared himself the winner of this election, has a long history in the country. He served under Mobutu Sese Seko, the dictator who ran Congo, then known as Zaire, for 32 years until Mobutu was overthrown in 1997 in a coup led by Kabila's father, Laurent.

A brutal civil war then broke out, lasting until 2003, in which 5 million people are estimated to have died, many from disease and starvation. Eight African nations took part in the war.

Conflicts still simmer in the northern and eastern regions of the country, with the United Nations regularly reporting incidents of massacres. Rape is commonly employed as a weapon of war.

The country, which is about two-thirds the size of Western Europe, was ranked last this year on the UN's Human Development Index, despite its mineral wealth. The minerals, however, help fuel the conflicts in the eastern regions.

Ntabo Ntaberi Cheka, a militia leader who is running for parliament in an eastern province, was added by the UN Security Council to its sanctions list on Tuesday for his alleged involvement in war crimes. He has not withdrawn his candidacy.

Kabila became president in 2001, taking over from his father, who was assassinated at the height of the civil war. The younger Kabila was elected in 2006, the country's first election. Those polls were organised by the international community.

Because the opposition vote is split, analysts expect Kabila to win, despite Tshisekedi's announcement of victory and his refusal to join calls for cancelling the vote.

CENI was quick to condemn Tshisekedi, whose supporters have already clashed with Kabila's camp in the run-up to election day. Police intervened with a heavy hand to stop the violence and 10 people were found dead in the aftermath.

Daniel Ngoy Mulunda, the head of CENI, said that only 450 polling stations did not function properly. While noting violent incidents in various regions, he did not think the elections should be called off.

“Despite the many obstacles facing the conduct of these elections, the voters have exhibited an extraordinary commitment to peace and democracy,” said the US-based Carter Center, which observed 300 polling stations.

The group called on politicians to remain committed to a peaceful process, amid growing concern for the country's future. Kabila's term ends next month, and the post must be filled.

“The stability of DRC is the stability of the subregion,” said Baya Kara, director of the Carter Center's election observation mission in the DR Congo. - Sapa-dpa