Seven people have been killed in two separate clashes on election day in the southeast of the Democratic Republic of Congo (DRC), the country's interior minister has said.
Although voting was scheduled to be completed early on Monday evening, the chairman of the country's electoral commission announced that voting would be extended at least until Tuesday.
Election-related violence occurred in the southern city of Lubumbashi on Monday, after armed men attacked a vehicle carrying ballots and several voting centres, Bikanga Kazadi told the AP news agency.
He said that the first attack happened before dawn when armed men opened fire on a vehicle loaded with voting materials, including ballots. Later in the day, armed men attacked voting centres.
Kazadi said the army was called in to quell the attack. One policeman and four assailants were killed, he said.
Separately, locals burnt down three polling stations in the neighbouring opposition heartland of West Kasai and an election observer was badly injured in crowd violence, electoral monitoring group RENOSEC said.
More than 31 million people are eligible to vote on Monday in the country's second elections since back-to-back wars from 1996 to 2003. The country remains one of the world's poorest despite an abundance of cobalt, copper, diamonds and gold.
About 19,000 candidates competing for 500 legislative seats, while 11 candidates are vying for the presidency.
The buildup to the vote has been dogged by concerns over whether the country is ready, as election officials raced up until the last moments to finish their preparations, amid rumours of electoral fraud.
In weekend clashes in the capital, Kinshasa, police and supporters of Etienne Tshisekedi, the main opposition candidate, left four people dead and prompted the UN to appeal for calm.
Fraud allegations have been raised ahead of the polls
"We've been able to speak to various candidates in this election. One is alleging systematic fraud by authorities to favor the incumbent," Al Jazeera's Yvonne Ndege, reporting from the capital, said. "He says children are being registered to vote and some ballots were filled out before the election."
"People see no reason to conduct an exercise in which the people's votes don't count ... [the fact that] the opposition is already presenting evidence of fraud is a warning of tension."
Our correspondent also said it was difficult to give a comprehensive account of election difficulties, since there were less than 1,000 election monitors for some 63,000 polling stations.
Cindy McCain said that observers had stumbled upon what may be a case of ballot stuffing in the east. The wife of US Sen John McCain is part of a team of independent observers.
"But I'm really hopeful," McCain told Al Jazeera. "What we've seen has not been perfect progress but a really good beginning."
In Goma, the main city in the east of the country and flagged as a possible election hotspot in a region of the country where many areas are still controlled by armed groups, people began arriving at polling stations on foot and motorcycle taxis before sunrise, Al Jazeera's Azad Essa reported.
"There is talk of burnt ballot sheets and missing names on voter rolls, which has also caused confusion and anger," he said. "Security also seems to have tightened up as we approach closing time, compared to earlier in the day."
Etienne Senga, 25, had arrived early "to beat the crowds" and said he hoped for peace, security and better economic opportunity.
Mapendo Furaha, 24, told Al Jazeera she intended to "vote for a new president" to replace incumbent Jospeh Kabila.
"In 2006 [the last elections] I was hoping for peace and development," she said.
"We have at least gained peace but the development didn't not happen ... Perhaps this time round it will."
Speaking to Al Jazeera, Anneke van Woudenberg, a senior researcher at Human Rights Watch, said: "It's a very slow start, and very chaotic. Quite a few offices are missing materials.
"People are patiently waiting, but it's unclear how long they will be willing to wait."
As of Monday afternoon, polling stations had still not opened in the Kenya neighborhood of Kinshasa because voting materials had not been delivered.
In Massina, another poor district near Kinshasa's airport, anger was beginning to boil over as voters continued to wait outside of still-unopened polling stations.
"Overall the biggest problems appear to be logistical," said Al Jazeera's Peter Greste. "And these are the kind of issues the opposition will pick up on and complain about."
Polls were expected to close at 600pm local time (1700GMT) and the presidential results are expected to be released on December 6, and the parliamentary results several weeks later.
The 40-year-old Kabila, who has been in power since 2001, is tipped to win the single-round poll and secure another five-year term.