Fire has gutted an electoral commission depot in Kinshasa, capital of the Democratic Republic of Congo, in the violent run-up to a presidential vote.

More than two-thirds of the electronic voting machines allocated for Kinshasa had been destroyed, an official said.

The cause of the fire has not been confirmed. Black smoke could still be seen over the site on Thursday morning.

The campaign to elect a successor to President Joseph Kabila on 23 December has been marred by deadly clashes.

The president's mandate ended in 2016, but elections have been repeatedly delayed.

Dozens of opposition supporters have been killed in protests demanding that he step down.

The fire at the electoral commission warehouse broke out at about 02:00 local time (01:00 GMT).

An electoral commission official said the blaze had destroyed about 8,000 electronic voting machines, representing two-thirds of the total required for Kinshasa. The capital of four million people is home to some 15% of the electorate.

The official described the fire as a major setback, but said efforts were being made to ensure the election went ahead as planned.

Spare voting machines would be retrieved from other parts of the country to make up the shortfall in the capital, he said.

The BBC's Louise Dewast in Kinshasa says several opposition candidates have called for the voting machines to be banned, as they believe they could be used to rig the vote.

The government has accused supporters of an opposition candidate, business tycoon Martin Fayulu, of starting the depot fire. Mr. Fayulu's campaign has rejected the charge.

Mr. Kabila is backing his former Interior Minister, Emmanuel Ramazani Shadary, in the election.

The vote is expected to be a tight contest between him, Mr. Fayulu, and opposition leader Felix Tshisekedi.

DR Congo has not had a peaceful, democratic transfer of power since independence from Belgium in 1960.