VATICAN CITY • Pope Francis yesterday opened the "Holy Door" in St Peter's Basilica, launching an extraordinary Catholic jubilee year dedicated to the theme of mercy.

"This is the door of the Lord. Open to me the gates of justice," the pontiff said before pushing the giant bronze doors open and, after a prayer, walking through them. Pope Francis was followed through the door by his predecessor, Benedict XVI.

Tens of thousands of Catholic pilgrims assembled at St Peter's Square in Rome to watch the opening of the usually bricked-up Holy Door, the start of the year-long religious event. In Catholic tradition, the opening of the Holy Door symbolises an invitation from the church to believers to enter into a renewed relationship with God.

The first pilgrims had gathered in the square since before dawn to witness the event, held under unprecedented security measures in the wake of recent terrorist attacks around the world. Police checked pilgrims, reporters, diplomats and even priests entering the area starting several blocks from the square.

During the year-long celebrations, one of the most important events in the 1.2 billion-member Roman Catholic Church, the faithful make pilgrimages to Rome and other religious sites around the world. This is only the 29th Holy Year in the Church since the tradition started more than 700 years ago.

Holy Years normally take place every 25 years unless a pope decrees an extraordinary one to bring attention to a particular need or topic. The next Holy Year had been scheduled for 2025 before Pope Francis, 78, decided to call a special one on the theme of mercy, a major part of his push for a less judgmental and more inclusive church.

The airspace over most of Rome was closed yesterday, and transport of petrol, gas, weapons, explosives and fireworks was banned. A no-go zone was instituted for vehicles around the Vatican and rubbish bins were sealed or removed.

"This security was necessary. It worked very well and it was worth it because we feel safe," said Mr Corrado De Gioia, who came to Rome from Treviso in northern Italy.

REUTERS, AGENCE FRANCE-PRESSE