The presidential election in the Democratic Republic of Congo – due to take place on Sunday – is being postponed until March in three areas.
The electoral commission blamed insecurity and an Ebola outbreak.
The decision appears to cancel the votes of more than a million people because the new president is due to be sworn in by the middle of January.
An opposition candidate, Martin Fayulu, earlier said any postponement would be an attempt to rig the election.
Mr Kabila, who has been in office since 2001, was meant to have stepped down in 2016 under a constitutional prohibition from seeking an additional term.
However, the election to choose his successor has been continually postponed, amid unrest and reported logistical difficulties. Opposition supporters suspect that he intends to cling on to power.
Why has voting been delayed in three areas?
The three areas are Beni and Butembo in eastern North Kivu Province and Yumbi in the west of the country.
In Yumbi, at least 80 people were killed earlier this month and thousands have fled to neighbouring Congo-Brazzaville amid violence triggered by a dispute over where to bury a traditional chief.
Beni has been affected by an Ebola outbreak that has killed at least 350 people since August. Nearby Butembo has seen attacks on civilians attributed to a Ugandan Islamist militia, the Allied Democratic Forces.
However the area is also seen as an opposition stronghold and opposition supporters accused the government of attempting to disenfranchise them.
Moise Katumbi, an opposition leader in exile who is supporting Mr Fayulu, said the move was “unjustifiable” and showed that “the regime wants to be in power forever to continue its pillage”.
Le report du vote à Beni, Butembo & Yumbi est injustifiable. Cette nouvelle manœuvre montre que le régime veut s’éterniser pour continuer le pillage !
Naanga & la CENI ont prouvé leur mauvaise foi & leur incompétence. Les Congolais doivent se prendre en main & chasser ce régime !— Moise Katumbi (@moise_katumbi) December 26, 2018
End of Twitter post by @moise_katumbi
Pro-democracy campaigner Leonnie Kandolo said publishing final results before all regions had voted showed the government was “taking us for idiots”.Skip Twitter post by @leonnie_kandolo
#RDC,Comment peut-on publier les résultats définitifs le 15 janvier, pendant que d’autres villes et territoires voterons en mars? On nous prend vraiment pour des c…!— Leonnie Kandolo (@leonnie_kandolo) December 26, 2018
End of Twitter post by @leonnie_kandolo
What other issues have there been?
On 21 December, the electoral commission said the vote was being delayed by another week, after admitting that it was not ready. The decision was condemned by opposition politicians.
A delay in deploying voting materials to polling sites after a fire was behind the postponement, officials said.
The blaze destroyed more than two-thirds of the electronic voting machines allocated for the capital Kinshasa, where four million people – 15% of the electorate – live, an official said.
Meanwhile the government has accused Mr Fayulu of instigating election violence. Mr Fayulu’s campaign has rejected the charge.
Mr Kabila is backing former Interior Minister Emmanuel Ramazani Shadary in the election.
DR Congo has not had an orderly change of government since it gained independence from Belgium in 1960.