Residents have been fleeing the Congolese capital, Kinshasa, amid fears of violence after election results that are due to be announced today.
The opposition, which has been warning for weeks that President Joseph Kabila planned to rig the outcome, is expected to take to the streets if he is declared the winner.
Outbound flights trebled in price over the weekend, many businesses shut and people bought emergency supplies as they prepared for clashes between opposition supporters and heavily armed security forces.
The 40-year-old president, who inherited power after his father was assassinated 10 years ago, was given a huge lead over veteran opposition leader Etienne Tshisekedi in partial results announced on Sunday.
But international observers fear the true results of a ballot that was meant to take 12 hours but stretched over four days will never been known.
In some areas, polling stations were burned down, voting cards were seized at gunpoint and accusations of pre-marked ballots were rife. An unknown number of votes have been lost.
Some blame poor preparation but others see a deliberate plan to steal the election by Mr Kabila, who has been accused of plundering Congo's mineral wealth to amass the war chest needed to stay in power.
Anger has risen in Kinshasa's slums after a killing spree by Mr Kabila's Republican Guard on the last day of campaigning that claimed the lives of at least 16 Tshisekedi supporters.