Pope Benedict XVI condemned the increasing commercialisation of Christmas as he celebrated Christmas Eve Mass, urging the faithful to look beyond the holiday's "superficial glitter" to discover its true meaning.

Benedict presided over the service in a packed St Peter's Basilica, kicking off an intense two weeks of Christmas-related public appearances that will test the 84-year-old pontiff's stamina amid signs that fatigue is starting to slow him down.

The Christmas Eve Mass was moved to 10pm from midnight several years ago to spare the Pope a late night that is followed by an important Christmas Day speech.

In a new concession this year, Benedict processed down the basilica's central aisle on a moving platform to spare him the long walk.

Benedict appeared tired by the end of the Mass and a dry cough interrupted his homily.

In his homily, Benedict lamented that Christmas has become an increasingly commercial celebration that obscures the simplicity of the message of Christ's birth.

"Let us ask the Lord to help us see through the superficial glitter of this season, and to discover behind it the child in the stable in Bethlehem, so as to find true joy and true light," he said.

It was the second time in as many days that Benedict has pointed to the need to rediscover faith to confront the problems facing the world today. In his end-of-year meeting with Vatican officials on Thursday, Benedict said Europe's financial crisis was largely "based on the ethical crisis looming over the Old Continent."

Benedict officially kicked off Christmas a few hours before the evening Mass, lighting a candle in his studio window overlooking St Peter's Square in a sign of peace, as crowds gathered to witness the unveiling of the Vatican's larger-than-life sized nativity scene.

Security was tight for the evening Mass, as it has been in recent years. There were no repeats of the 2008 and 2009 Christmas Eve security breaches, in which a woman with a history of psychiatric problems and wearing a telltale red sweatshirt jumped the wooden security barrier along the basilica's central aisle and lunged for the Pope.

In 2008, the Pope's security detail blocked her from getting to Benedict. But in 2009, she managed to grab Benedict's vestments and pulled him to the ground. The Pope was unhurt and continued along with the service, but a French cardinal who was nearby fell and broke his hip.

On Sunday, Benedict will deliver his traditional "Urbi et Orbi" speech, Latin for "to the city and the world" from the central loggia of St Peter's overlooking the piazza. Usually, the speech is a survey of sorts of the hardships and wars confronting humanity. He is also due to deliver Christmas greetings in dozens of languages.

Next weekend, he will preside over a New Year's Eve vespers service, followed by a New Year's Day Mass. A few days later he will celebrate Epiphany Mass followed by his traditional baptising of babies in the Vatican's frescoed Sistine Chapel.