- Some polling stations did not open all day, leading to widespread frustration. Voting has been extended into Thursday in some areas.
- Four opposition candidates have called for the election to be cancelled
Voting in the Democratic Republic of Congo's high-stakes presidential election has been marred by lengthy delays and claims of fraud.
Some polling stations did not open all day, leading to widespread frustration. Voting has been extended into Thursday in some areas.
Four opposition candidates have called for the election to be cancelled.
One of them described the poll as "total chaos", following violence during the campaign.
President Félix Tshisekedi faces 18 candidates as he seeks a second term.
Some 44 million people were eligible to cast their ballots, following a campaign dominated by worsening conflict in the mineral-rich east.
DR Congo is roughly four times the size of France, but lacks basic infrastructure - even some of its main cities are not linked by road. About two-thirds of the country's 100 million population live below the poverty line, earning $2.15 (£1.7) a day or less.
The UN, Egypt and neighbouring Congo-Brazzaville helped fly election material to remote areas.
Polls had been due to open at 06:00 local time (04:00 GMT in Goma; 05:00 GMT in Kinshasa), and close after 11 hours. But widespread delays were reported.
One woman in Kinshasa told the BBC she had had to fight inside the polling in order to vote. "There was chaos," she said. "I was trampled under foot."
Another voter said he went home after polls still hadn't opened by 18:00 local time, when there was a power cut. "Some people have been here since 04:00 but we were told there was a problem with the machines," he told the BBC.
Opposition presidential candidate Martin Fayulu, runner-up in the disputed 2018 presidential election, described the situation as "total chaos".
"If all the people don't vote in all the polling stations indicated by the Ceni [Independent National Electoral Commission], we won't accept these elections," he was quoted as saying by Reuters after voting in the capital.
The news agency reported that another presidential candidate, Nobel Peace Laureate Denis Mukwege, alleged that the "electoral fraud of the century [was] taking place".
Mr Fayulu and Mr Mukwege were joined by two other candidates in calling for a rerun of the poll.
Millionaire businessman Moïse Katumbi said it was too soon to judge but there had been "many failures".
Ceni official Patricia Nseya acknowledged cases of misconduct among her staff and promised sanctions following ongoing investigations.
According to the Symocel observer group, nearly 60% of polling stations opened late, while 30% of voter material was defective.
Election chief Denis Kadima said the election would be extended into Thursday in those areas where voting did not happen on Wednesday.
He also confirmed that there were at least 3,244 attempts at hacking the institution's computer systems.
In the north-eastern town of Bunia, people who had previously fled the violence and couldn't travel back to their home villages to vote expressed their anger by attacking a polling station and destroying voting machines before police restored order.
There are some places where voting is not taking place at all because of rebel activity.
Ceni is expected to announce provisional results on 31 December.
DR Congo sits on vast reserves of cobalt, currently a vital part of many lithium batteries, seen as essential to a future free of fossil fuels.
For the first time, Congolese nationals living in five other countries - including South Africa and former colonial power Belgium - are able to cast their ballots.
As before, the winner will be the candidate with the most votes, with no run-off if they fail to cross the 50% mark. The large number of challengers to Mr Tshisekedi could work to his advantage, as it may divide opposition support.
Voters are also choosing parliamentary, provincial and municipal representatives - with about 100,000 candidates in total - in this huge country, which stretches some 2,000km (1,400 miles) west to east.
There are more than 175,000 polling booths. The electoral commission, with the help of UN peacekeepers, began delivering voting material in far-flung areas about two months ago because of the poor transport network.
In the east, insecurity has dominated the run-up to the polls.
Dozens of armed groups have been competing to control parts of the mineral-rich region.
The presence of a UN peacekeeping force, an East African regional force and Congolese soldiers has not quelled the violence, which has resulted in about seven million people being forced from their homes. Many of those have not been able to register to vote, in what some criticised as a chaotic registration process.
Political violence in the run-up to the polls was also a source of concern.
On the eve of the vote, the European Union said it was worried about "the hate speech, violence and incidents that have marked the last few days". There have been some deadly incidents, causing Mr Katumbi to briefly suspend his campaign.