France has agreed to increase the number of troops in its former colony by the end of the year, under a UN resolution, to help prevent the state spiralling out of control, with the risk the power vacuum could encourage militancy.
The Central African Republic has descended into chaos since Muslim Seleka rebels ousted President Francois Bozize in March.
"There is a political emergency because there is no state," Mr Hollande said as he spoke in Pretoria alongside South African President Jacob Zuma.
"There is also an emergency at a regional level because there is a risk of spillover. We might witness religious conflict."
There have already been sectarian clashes in the conflict that has driven more than 400,000 people from their homes, fleeing violence including murder and rape.
France has about 400 troops in the capital, Bangui, and sources have told Reuters their numbers could be increased to around 750.
However, Paris is reluctant to be left to deal with another African hot spot after it felt allies such as the US were hesitant to help it halt a rebel advance by al Qaeda-linked insurgents in Mali earlier this year.
The Central African Republic is geographically at the centre of what some strategists have called an "arc of insecurity" of Islamist fighters that cuts from Kenya and Somalia in east Africa across to Mauritania in the west.
Mr Zuma said he agreed intervention was needed, he stopped short of saying Pretoria would send more troops.