Few Congolese benefit from the country's mineral wealth
Voting has been mostly peaceful but at least one person died in protests over alleged fraud in the north-east.
Results are not expected to be announced for about a week.
Congolese hope the election will end years of conflict and abuse of power. Incumbent President Joseph Kabila faces ex-rebel Jean-Pierre Bemba.
The run-off concludes DR Congo's first fully democratic polls since independence in 1960 and is supposed to draw a line under a five-year conflict.
'For the people'
Voting started slowly in the capital, Kinshasa, and other western areas because of a violent thunderstorm.
Turn-out is reported to be lower across the country, compared to July's first round.
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In the north-eastern town of Bumba, supporters of Mr Bemba burnt ballot boxes, after claims of vote-rigging, AP reports.
"Two people were killed when the police opened fire to disperse the crowds," local Equateur province governor Yves Mobando told Reuters but a UN spokeswoman said only one person had died.
Shots were also fired at a polling station in Kinshasa following claims of attempted fraud.
The BBC's Mark Doyle in Kinshasa says it is impossible to exaggerate how the destiny of DR Congo could shape the future of Africa.
Nine states border the country and all were affected by the wars caused by the long lack of real government in DR Congo, the power vacuum at the heart of Africa, he says.
Some four million people are thought to have died.
Its rich reserves of minerals such as gold, diamonds and coltan - used in mobile phones - have attracted a series of armed groups, both Congolese and foreign, intent on looting.
DR Congo is two-thirds the size of Western Europe but has just 300 miles of paved roads after years of conflict and gross mismanagement.
UN officials say the polls are the most important on the continent since the 1994 election that ended apartheid in South Africa.
Polls were due to start closing at 1500 GMT in the east and an hour later in the west, but voting was extended in some areas.
Troops standby
Mr Kabila has strong support in the east of Congo; Mr Bemba is popular in the west.
Many easterners credit Mr Kabila with ending the war and blame the conflict on rebels such as Mr Bemba.
FIRST ROUND RESULTS DR CONGO WAR 1998 - 2002 4m dead At least 8 armies, many rebel groups 2003: Rebels join unity government East remains unstable 17,000 UN peacekeepers
Mr Kabila won first round polls on 30 July, but fell just short of the 50% needed for outright victory.
He has also gained the support of the candidates who came third and fourth - veteran nationalist Antoine Gizenga and Nzanga Mobutu, son of the country's long-time leader, Mobutu Sese Seko.
At least 23 people were killed in armed clashes between security forces loyal to Mr Kabila and Mr Bemba in Kinshasa after the results were announced.
United Nations Secretary General Kofi Annan has called on the two candidates to ensure that the election progress passes off peacefully.
Both men have promised to urge their supporters against violence and to abide by election rules.
Extra UN peacekeeping troops are on standby in the east of the country.
In Kinshasa, the UN is being backed up by a special European Union military force.
The final round of voting has ended in the first free elections in the Democratic Republic of Congo (DRC) in over forty years. 

The runoff is between incumbent President Joseph Kabila and Vice-President Jean-Pierre Bemba, who led a field of 33 candidates in the first round of polling held on July 30, but failed to achieve the required majority vote. The voting has been largely peaceful, though isolated incidents of violence and voting fraud have been reported.




 Contestants Bemba (left) and Kabila, August 2006.Credit: MONUC/Myiram Asmani/IRIN



 '''Jean-Pierre Bemba''' 

 '''Joseph Kabila'''



 44 years old 

 35 years  old 



  One of four Vice Presidents 

 President 



 leads Movement for the Liberation of Congo 

 leads People's Party for Reconstruction and Democracy



 polled  20% of vote in first round 

 polled 44.8% in first round 



 Main support base in western Congo 

 Main support base in eastern Swahili-speaking Congo



 son of a prominent businessman, who was close to Mobutu Sese Seko. backed by Ugandan army during the war. retains considerable business interests. 

 son of former President Laurent Kabila, grew up abroad, received wartime backing from Rwanda.