VATICAN CITY (AFP) - Pope Benedict XVI left the Vatican on Thursday for the last time as pontiff before he steps down as leader of the world's 1.2 billion Catholics, becoming the first pope to resign in 700 years.

Benedict boarded a white helicopter emblazoned with the Vatican flag for the papal summer residence of Castel Gandolfo near Rome, flying over the Vatican for the last time as pope.

As he took leave of his closest aides in an emotional parting ceremony in the Vatican, staff lined the route of his motorcade and applauded.

The bells of St Peter's Basilica rang out as the helicopter took off from the Vatican's helipad.

"Thank you for your love and support," the pope said in a final tweet sent from his @pontifex Twitter account just before taking off.

"May you always experience the joy that comes from putting Christ at the centre of your lives." The Twitter account will now be suspended until a new pope is elected in a conclave next month.

The 85-year-old, who has said he can no longer carry on, will then bid one last goodbye to residents of Castel Gandolfo before retiring out of the public eye forever to a life of prayer.

At 1900 GMT, Benedict will no longer be pope.

The Swiss Guards - a military corps that has protected the papacy since the 15th century and is best known for its brightly-coloured uniforms - will then leave their posts and return to Rome.

Following tradition, staff in the Vatican will meanwhile apply seals to the doors of the papal apartments and the lift that leads up to them - to be broken only once a new pope has been elected.

Benedict is only the second pope to resign in the Church's 2,000-year history and in his final hours as pope on Thursday, he took the unprecedented step of pledging allegiance to his successor.

"Among you, there is also the future pope to whom I promise my unconditional obedience and reverence," the pope said as he bade farewell to cardinals in the Vatican's ornate Clementine Hall.