Argentina's Jorge Mario Bergoglio was elected Pope Francis I on Wednesday, becoming the first Latin American pontiff in a surprise decision that raised the prospect of a more open Catholic Church.
The 76-year-old moderate emerged smiling on to the balcony of St Peter's Basilica to the cry of "Habemus Papam!" ("We Have a Pope!"), as tens of thousands of pilgrims cheered, cried and applauded.
Francis called for "brotherhood" among the Church's 1.2 billion Catholics and prayed the Hail Mary together with the crowd in St Peter's Square.
He said he felt as if cardinals had gone to "the other end of the world" to find him -- and across the Atlantic Ocean in Buenos Aires celebrations erupted.
Francis also publicly thanked his predecessor Benedict XVI, who shocked the world by resigning last month in a move unseen for seven centuries.
The historic election after 85-year-old Benedict's abrupt resignation last month was being followed around the world on live television as well as through social media and smartphone apps -- this is the first ever tweeted conclave.
The papal Twitter account @pontifex announced his name in Latin: "Habemus Papam Franciscum".
Latin America has the highest number of Catholics in the world and there had been growing calls for the new pope to come from the southern hemisphere for the first time but Bergoglio was never considered one of the frontrunners.
"I can't believe it! An Argentinian pope!" said Silvia Pastormerlo, a 50-year-old from Argentina in St Peter's Square.
Also in the crowd was Julio Cesar Attaremo, a 42-year-old notary from Santa Fe, in Argentina. "We're very happy and proud, not just for Argentina but for the whole of South America," he said.
"Bergoglio has character. He's very humble and he's someone who really goes out to the people."
The new pope is seen as austere and media-shy. He is believed to have been the runner-up at the conclave in 2005 that elected Benedict -- although details of the deliberations are secret.
White smoke earlier billowed from the chimney on the Sistine Chapel and the bells of St Peter's Basilica rang out, signalling the election had taken place after five rounds of voting -- one more than when Benedict was elected.
Bergoglio is the first Jesuit to become pope.
The Argentinian of Italian descent, who is the 266th pope in the Catholic Church's 2,000-year history, retired to a chamber known as the "Room of Tears" immediately after the nomination to don his white papal vestments and then prayed in the Pauline Chapel.
Bells pealed in churches across Italy to celebrate the announcement and residents of Rome raced to the floodlit 17th-century Vatican plaza, running out of their homes and cafes to reach the square in time.
Cardinals have been locked up behind the Vatican walls and cut off from the outside world since Tuesday, meeting in a sublime Renaissance chapel swept for recording devices and installed with scramblers to prevent any communication.
Pilgrims in the square had braved rain that had fallen most of the afternoon, but it stopped after the election of a pope was announced by the white smoke.
"I didn't think I would cry but I guess the adrenaline's taking over!" said Rebecca Hine, a student from Canada.
Benedict's eight-year papacy was riven by scandals and the new pope will face immediate challenges -- stamp his authority on the Vatican machinery and try to bring back a Catholic flock that is deserting churches across the West.
Benedict's style was often seen as too academic and he was never as popular as his predecessor Pope John Paul II. Many of the cardinals have called for the new pope to be a better communicator, able to reach out particularly to young people.
Conclaves are usually only held after a pope dies and are sometimes decades apart -- the last one was in 2005, the one before that 1978. A popular Italian expression for things that happen very rarely is "at every death of a pope".
But the 85-year-old Benedict broke with tradition, becoming the first pontiff to resign since the Middle Ages. He has said he will retire to a former nunnery inside the Vatican -- an unprecedented and delicate situation for the Church.
In one of his last acts as pope, he issued a decree allowing cardinals to bring forward the date of a conclave in the event of a pope's resignation -- a move seen by many as potentially setting a precedent for ageing pontiffs in the future.
The scandal of hushed-up sexual abuses of children by paedophile priests going back decades has also cast its shadow over the conclave.
The US group SNAP (Survivors Network of those Abused by Priests) called for over a dozen cardinals to be excluded from the deliberations either for covering up abuses or for making tactless remarks about the scandals.
Vatican spokesman Federico Lombardi on Wednesday defended the cardinals and accused SNAP and other activists of showing "negative prejudices".
"None of us are surprised that they have tried to take advantage of these days to repeat their accusations and give them greater resonance," he said.