French troops have started deploying in the Central African Republic to beef up a UN-backed military operation as President Hollande welcomed 40 representatives of African countries to a conference of peace and security in Paris.

Defence minister Jean-Yves Le Drian said that 650 troops already in the country had started operations to protect civilians and restore security after more than 100 people died in fighting in the capital of Bangui.

"The operation has begun insofar as the French forces that were already present at Bangui airport with a mandate limited to protect that airport and our nationals last night started patrols in Bangui," Le Drian told Radio France Internationale.

France was expected to double its contingent on the ground.

"You have to secure, you have to disarm," Le Drian siad. "You have to ensure that the vandals, the bandits, the militias know they can't use the streets of Bangui for their battles."

The UN Security Council authorised a joint operation by France and the African Union after violent clashes between Christian fighters backing deposed president Francois Bozize and Muslim militia supporting the government of President Michel Djotodia erupted in Bangui.

The African Union will add 1,000 troops to its 2,500-strong force.

Bangui was reportedly calm but thousands of residents crowded into a field outside the airport to ask for shelter and protection by French troops.

Le Drian said that French soldiers had opened fire on a pickup truck approaching the airport and killed several alleged militiamen on board.

Security in CAR deteriorated after Bozize was ousted by Djotodia through a military coup in March.

Djotodia headed the Seleka rebel coalition, which was made up of mostly Muslims, and appointed himself as the first Muslim president of CAR. Half of the country's 4.5m population is Christian, while about 15% is Muslim.

The move sparked the creation of the so-called "anti-balaka" (machete in the local Sango language) Christian self-defence force.

Both factions have been accused of atrocities against the population.

Among the delegates at the Paris conference was CAR prime minister Nicolas Tiangaye who welcomed France intervention and called for international support.

"We also need massive humanitarian aid from the international community," Tiangaye said. "There is a risk of famine."

Security in Mali and Libya was also high on the meeting's agenda.

Hollande Elysee Tiangaye
France\'s President Francois Hollande greets prime minister of the Central African Republic Nicolas Tiangaye at the Elysee Palace (Reuters)