Fighters backing Alassane Ouattara, Cote d'Ivoire's internationally recognised president, are attacking the residence of the incumbent, Laurent Gbagbo, in the city of Abidjan.
An Ouattara spokesman said they are meeting some resistance though his forces swept into the commercial capital on Thursday, and have also taken control of the state TV broadcaster.
It is being described as a final push to unseat the entrenched ruler.
Gbagbo has refused to give up power despite losing last November's election, according to results verified by local and international officials.
Al Jazeera's Khadija Margadie reports.