photo - PAP/EPA
The 85-year-old Benedict XVI became Pope after the death of John Paul II in April 2005.
The Italian newspaper Corriere della Sera is reporting that the German Pope told a congregation of cardinals in Rome, in Latin, that “I do not feel strong enough to continue”.
"After repeated consultation with my conscience before God, I gained confidence that because of advanced age my strength is not enough to adequately serve the ministry of St Peter," Benedict XVI said.
Benedict XVI also thanked support shown to him during his pontificate and asked for forgiveness for any failings and "imperfections", according to Radio Vatican.
“The abdication of Pope Benedict XVI is a great surprise to all of us,” said Secretary of the Polish Episcopal Conference, Bishop Wojciech Polak.
Italian cardinal Angelo Sodano has said the news is "like a bolt from the blue”.
Theologian and journalist Father Wacław Oszajca told the Polish PAP news agency that “I do not think this is the result of health issues alone, but demonstrates a sense of responsibility to the Church”.
"He must have had good reasons to resign," he added.
Pope Benedict visited Poland on his second ever trip abroad as Pontiff in 2005.
A conclave of cardinals will gather to choose a new Pope in March.
Vatican spokesman Father Federico Lombardi said Benedict XVI will not take part in the conclave.
This is the first time in the modern-era that a Pope has resigned.
The last pontiff to resign was Pope Gregory XII, who stepped down in 1415.
Pope Benedict's time as Pontiff was dogged by accusations of child abuse within the Church and he was personally accused of covering up the extent of the scandal.
Religious sociologist, Prof. Wojciech Świątkiewicz from the University of Silesia in Katowice, has said that the next Pope “will probably be younger”, reminding that Benedict XVI was 78 years-old when taking over at the head of the Roman Catholic Church.
The professor speculated that perhaps the Pontiff felt the modern age passing him by.
“The contemporary world is experiencing a revolution in the cultural sphere, associated with rapid changes in communication. I do not want to say that Pope Benedict XVI did not understand this, but for him this generation is remote and it is probably better if he is succeeded by someone from the younger generation," he said. (pg)