Protected by the heaviest security ever seen on his trips, Pope Francis on Sunday preached reconciliation in the divided Central African Republic, a nation racked by bloodshed between Muslims and Christians.

As the pope's Alitalia plane touched down from Uganda to start his first visit to a war zone, attack helicopters patrolled the skies and armoured personnel carriers from French and UN peacekeeping forces waited outside the airport.

Special security forces wearing patches of the yellow and white colours of the Vatican flag were on hand to help his normal security retinue.

In an unprecedented precaution for papal trips, a UN soldier armed with a rifle rode in each of the minibuses carrying reporters accompanying the pope.

Bangui, the capital of the former French colony, has seen a surge in clashes that have left at least 100 people dead since late September.

France, which has around 900 soldiers deployed in the country, warned the Vatican this month that the visit could be risky but the pope was determined to go to the majority Christian nation.

"Reconciliation, forgiveness, love, peace," he said in a dramatic voice in the homily of a Mass at the city's cathedral in the afternoon, appealing to warring militias to "lay down these instruments of death".

Francis was driven past tens of thousands of cheering people to and from events in a simple car or an open popemobile.

"Work, pray, do everything for peace. But remember, peace without love, friendship and tolerance is nothing," he said at one stop, a visit to camp housing some 4,000 people displaced by the violence in Bangui's neighbourhoods.

He was mobbed by the crowd and asked them all to shout out repeatedly in their native Songo language: "We are all brothers".

tight security continued in the afternoon when he opened a "holy door" at the city's cathedral for a symbolic local start of the Roman Catholic Church's jubilee year on the theme of mercy. The jubilee begins officially at the Vatican on December 8.

"The Holy Year of Mercy is coming early to this land that has been suffering for years from hate, incomprehension and lack of peace," he said, standing on the cathedral steps.

"For Bangui, for all the people of the Central African Republic and for all the countries in the world suffering from war, we ask for peace," he said in the unprepared remarks to a crowd outside.

Hardened hearts

Shortly after his arrival Francis heard interim head of state Catherine Samba-Panza paint a bleak picture of her country.

"We absolutely need forgiveness because our hearts have been hardened by the forces of evil. We have lost the sincere love for others and we are henceforth anchored in intolerance, the loss of our values and the disorder that is the result," she told him at the official welcoming ceremony.

France sent in soldiers in 2013 in an attempt to stem the violence. Muslims and Christians have since split into segregated communities. Tens of thousands of Muslims have fled to the far north, creating a de facto partition.

About 80 per cent of the impoverished country's population is Christian, roughly 15 per cent is Muslim and five per cent animist.

Central African Republic's government is deploying around 500 police and gendarmes to secure the visit. More than 3,000 peacekeepers from the MINUSCA U.N. mission will also be deployed and French troops will be on alert as well.

The most dangerous segment of the pope's African trip takes place today when he will enter Bangui's PK5 Muslim enclave and visit its central mosque. The neighbourhood, epicentre of a fresh surge in violence, is encircled by Christian militias who have imposed a blockade.

Bangui is the final leg of his first African trip that has already taken him to Kenya and Uganda.