(CNN) -- Vote counting was under way Tuesday in the Democratic Republic of Congo after millions went to the polls in the giant nation's second postwar election amid logistical challenges.
Voting was extended for a second day Tuesday in some polling stations that experienced delays, including in the capital, which had heavy police presence.
In polling stations that opened on time, election workers were counting the votes.
Citizens lined up Monday to vote in the presidential and parliamentary polls nationwide.
In the capital of Kinshasa, citizens waded through muddy roads to cast their votes in an election that has sparked tension in the central African nation.
"Some had traveled for days using motorcycle taxis and bicycles to reach polling stations," said Herman Nzeza, the Congo representative of FreeFair DRC, a nonpartisan group that raises awareness of the election.
"That's why it was even more frustrating for them to get there and find their names missing. Some were being sent to other polling stations to find their names ... I saw women carrying babies walking in the mud to get to the next polling stations."
With more than 30 million voters, thousands of polling stations and lack of paved roads and basic infrastructure, Congo's elections were a logistical nightmare.
Issues included tardy election workers and blackouts at the end of the day despite extended vote hours, said Nzeza, who visited polling stations in the capital.
"We don't know what was happening to the ballots when the lights were off," he said.
There were also claims of ballot stuffing and the denial of poll access to registered voters in some areas, according to FreeFair DRC.
Nzeza said his organization got reports of three deaths in Katanga over election-related chaos, and was working to get more information.
Stacks of ballots with long lists of the more than 18,000 people running for 500 parliamentary seats was also a challenge for the nation whose majority citizens don't have access to education.
The presidential and parliamentary polls are critical in the central African nation struggling to rebuild years after a conflict left millions dead and displaced entire regions.
Incumbent Joseph Kabila, who took over after his father died in 2001 and was elected in Congo's first democratic election five years later, is one of 11 presidential contenders.
Supporters of leading opposition candidate, Etienne Tshisekedi, have vowed to take to the streets in protest if the polls are not fair.
"This is our version of the Arab uprising ... we want him (the incumbent) out. This country is rich in resources, but we have turned into world spectators. This frustration has lasted too long," said Paul Efambe, 42, who lives in the capital Kinshasa.
Fraud allegations started before the vote.
The opposition maintains that the leader of the electoral commission was picked by Kabila and thus cannot conduct a fair election, said Albert Moleka, a spokesman for Tshisekedi.
Tshisekedi's party had called for delayed poll, saying the government does not have adequate resources to meet the election needs.
"No country is perfect, but we should be able to conduct organized elections. We should respect the rights of the Congolese to have good elections, and our country does not have the facilities -- even roads -- to do that," he said.
Analysts fear the election outcome could plunge the nation into chaos again years after a 1998-2003 conflict that left 5 million dead as a result of fighting, diseases and starvation.
Clashes have erupted in days leading up to the vote, with at least two people killed when supporters of the two frontrunners hurled rocks at one another Saturday, Human Rights Watch said.
Stability in Congo -- which borders nine mostly vulnerable countries -- is vital to Africa's Great Lakes region. The years of war affected at least six neighboring nations, some of which are still battling rebel movements spawned during the conflict.
Despite Congo's vast resources including cobalt, gold, copper and tantalum, the fledgling democracy is mired in poverty and conflict especially in its eastern region, a hot spot for the so-called "conflict minerals" that activists say are used to fund rebel movements in the area.
Results are scheduled to be announced on December 6.