The Prime Minister of the Central African Republic has appealed to France and African nations to take immediate action to stem worsening sectarian violence in the country.

Nicolas Tiangaye made the calls as at least 105 people have been killed in fighting between former rebels and a mix of local militia and fighters loyal to ousted president Francois Bozize.

The UN has authorised French military action to halt Muslim-Christian sectarian violence that threatens to escalate into widespread civilian massacres.

Many of the dead are civilians, a Reuters witness and an aid worker said.

Mindful of the 1994 genocide in Rwanda, when hundreds of thousands were killed as the world looked on, the United States and other Western powers have urged swift international action to prevent the anarchy leading to major atrocities against the civilian population.

Most of the fighting in Bangui had eased by midday, though the streets were largely deserted and death tolls mounted and there were reports of widespread abuses during the fighting.

"We've received numerous reports from very credible sources of extrajudicial executions," said Joanne Mariner, a crisis expert with Amnesty International who is currently in Bangui.

"This underscores the need for international troops to arrive and secure the city. The situation is quickly spiralling out of control," Mariner added.

53 bodies had been brought to a mosque in Bangui's PK5 neighbourhood. Most victims appeared to have been clubbed or hacked to death, a Reuters witness at the scene said.

Samuel Hanryon, who works for medical charity Medecins Sans Frontieres at Bangui's Hopital Communautaire, said there were another 52 bodies at the morgue there.

The former French colony has slipped into chaos since mainly Muslim rebels seized power in March, leading to tit-for-tat sectarian violence.

Underscoring the scope of the violence, African peacekeepers protecting hundreds of civilians in their base in Bossangoa came under heavy fire from the mainly Muslim former rebels.

In New York, the UN Security Council authorized French and African troops to use force to protect civilians.

An arms embargo was imposed on the country and the Council asked the United Nations to prepare for a possible peacekeeping mission.

France has about 650 troops based at Bangui airport. Some 250 of these were deployed in town on Thursday to protect French interests and citizens.

French Foreign Minister Laurent Fabius said troop numbers would reach 1,200 "relatively quickly".

Central African Republic is rich in gold, diamonds and uranium but decades of instability and spill over from conflicts in its larger neighbours have kept it mired in crisis.

Michel Djotodia, leader of the Seleka former rebel alliance,is now the country's interim president but he has struggled to control his loose band of fighters, many of whom are gunmen from neighbouring Chad and Sudan.

Mainly Christian local defence groups, known as "anti-balaka", have sprung up in response to abuses committed in Bangui and up-country by the former rebels.