Pope Francis has marked his one-year anniversary with a simple tweet: "Please pray for me."

His appeal echoed his gesture on that rainy night one year ago when he came out on to the balcony of St Peter's Basilica and introduced himself to the world.

Rather than impart a blessing on the worshippers below him, Francis asked first for a "favour" from the crowd, bowing his head and asking his audience to bless him.

Francis has continued to ask for prayers, ending nearly every appearance with a similar request.

Francis was spending his anniversary on retreat south of Rome with senior Vatican cardinals and officials.

The Vatican said nothing special was planned to mark the date, just prayers.