Vatican City (AFP) - Christmas festivities will seem empty in a world which has chosen "war and hate", Pope Francis said Thursday.

"Christmas is approaching: there will be lights, parties, Christmas trees and nativity scenes ... it's all a charade. The world continues to go to war. The world has not chosen a peaceful path," he said in a sermon.

"There are wars today everywhere, and hate," he said after the worst terror attack in French history, the bombing of a Russian airliner, a double suicide bombing in Lebanon, and a series of other deadly strikes.

"We should ask for the grace to weep for this world, which does not recognise the path to peace. To weep for those who live for war and have the cynicism to deny it," the Argentine pontiff said, adding: "God weeps, Jesus weeps".

The sermon threw a shadow over the start of the festive season at the Vatican, where a giant Christmas tree was unveiled.

The 25-metre (82-foot) high pine hails from former pope Benedict XVI's homeland, the German state of Bavaria.

The tree, which will be decorated in time for the start of the Vatican's Holy Year on December 8, will be festooned with ornaments made by children from cancer wards in hospitals across Italy.

This year's nativity scene will be made up of 24 life-size figures, sculpted from wood and hand-painted.

In a nod to Pope Francis's humble style, alongside the figures from the story of Jesus's birth will be sculptures of ordinary people, including a man supporting an elderly person in need.