With the withdrawal of Delly Sesanga - a lawyer and MP from Kasai-Central province - there are now 21 opposition candidates running for the top job.

They will be competing against the incumbent President Felix Tshisekedi, who is vying for a second term in office.

Mr Sesanga’s withdrawal is seen as boosting opposition unity after former prime minister Matata Ponyo and two other candidates, Seth Kikuni and Franck Diongo, earlier endorsed Mr Katumbi.

“I have decided in the spirit of national unity to combine our forces to support the candidacy of Moise Katumbi,” he said on Sunday, while calling for his supporters to vote for him.

There had been discussions in the South African capital Pretoria with the aim of choosing one opposition candidate to face Mr Tshisekedi, which ended on 17 November without reaching a deal.

Campaigns for the elections started two weeks ago and end on 18 December – two days before the 20 December elections.

The campaign period has already witnessed deaths, with six killed in stampede on Saturday at Mr Tshisekedi’s campaign rally in Mbanza-Ngungu city in the west.

Earlier on Tuesday, a supporter of Mr Katumbi was killed at a rally amid clashes with supporters of the ruling party in the eastern Maniema province.