Goma, Congo (CNN) Citizens of the Democratic Republic of the Congo headed to the polls Sunday for a long-delayed presidential election originally scheduled to be held in 2016.

Voters lined up to pick a successor to President Joseph Kabila, who has ruled the central African country since 2001. Sunday's vote would have marked the country's first-ever democratic transfer of power, but an electoral commission's decision to delay voting in three opposition strongholds has all but guaranteed contested results.

Kabila has ruled Congo for nearly two decades. He came to power at 29 and amid crisis after the assassination of his father in 2001.

Although his second term ended in 2016, Kabila has refused to step down, clinging to power by violently cracking down on protests and suppressing the opposition. It was a surprise when the strongman announced in August that he would not seek reelection

On Sunday, Kabila promised the elections "will definitely be free and fair," adding his main concern was "very heavy rain" in the capital city of Kinshasa.

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