Argentinian cardinal Jorge Mario Bergoglio has been elected as the new leader of the Catholic church to succeed Pope Benedict who resigned last month.
White smoke billowing from the chimney of the Sistine Chapel at the Vatican early on Wednesday evening signalled that the Archbishop of Bueno Aires had been elected Pope by the conclave.
Pope Francis I greets the crowds for the first time in St Peter's Square
The news was met with roars and cheers from the huge crowd that had filled St Peter's Square since Tuesday when the cardinals began their deliberations to choose their new leader. Reports on Twitter talked of motorists abandoning their cars and racing to join the crowds.
The breakthrough came after the second vote on the second day of the gathering of the cardinals in Rome.
Seventy-six-year-old Bergoglio will be known as Francis I and is the first Pope to be chosen from outside Europe for more than a millennium.
He came second in the conclave which chose Pope Benedict XVI, who retired last month.
Although it was clear the Catholic church had chosen a new leader, the name of the new Pope was not revealed until 7.12pm UK time when Cardinal Jean-Louis Pierre Tauran, the president of the Pontifical Couincil, appeared on the balcony of the Vatican to announce to the thousands below that the church had '"an Argentinian Pope".
Huge crowds waited for the new Pope to be revealed
Ten minutes later, Pope Francis appeared to huge acclaim and thanked the crowds for their "warm reception".
He then thanked his predecessor before leading the crowd in the Lord's Prayer. He also asked them to pray for him.
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The conclave of 115 cardinals to choose a new leader for the world's 1.2 billion Catholics was prompted by the dramatic resignation of Pope Benedict last month.
His resignation threw the church into turmoil and exposed deep divisions among cardinals tasked with finding a manager to clean up a Vatican bureaucracy embroiled in recent scandals.
The new pope, the 266th, will be tasked with reviving Catholicism in a time of growing secularism.
Elected on the fifth ballot, Pope Francis was chosen in one of the fastest conclaves in years, something of a surprise given there was no clear front-runner going into the vote. The winner had to receive 77 votes, or two-thirds of the 115, to be elected.
Prime minister David Cameron reacted to the news on Twiter, describing it as "a momentous day":
The Archbishop of Westminster, Vincent Nichols, expressed his surprise over the cardinals' choice. Talking to Sky News, the leader of Britain's catholics said Pope Francis' election was also "very, very exciting".
"I look forward to his leadership," he added.
Cardinal Cormac Murphy-O'Connor, the former head of the Roman Catholic Church in England and Wales, said the new Pope was an "inspired" choice.
"He is a humble, gentle and very intelligent and spiritual man," he told Channel 4 News.
"I think that Pope Francis is going to be a blessing for the Catholic Church and for the world. Many will think it is a surprise choice, for me it is an inspired choice."
He told the BBC: "I think he will bring a new kind of style to the Catholic Church. Here is a man who has experienced over many years, especially in his own country but also elsewhere, something of the love for poor people.
"His own simplicity of life, I think, will be a great example to people. For many people this may be a surprise election but for me it is inspired and I am very very happy, not only for the Catholic Church, but for the world."
Kevin Flaherty, editor of The Catholic Times, said: "Cardinal Bergoglio has had a growing reputation as a very spiritual man with a talent for pastoral leadership serving in a region with the largest number of the world's Catholics.
"Since 1998, he has been the Archbishop of Buenos Aires, but he remains close to the people.
"He travels by bus, visits the poor, lives simply and even cooks his own meals.
"In choosing the name Francis - after St Francis of Assisi - 'Fr Jorge', as the people still call him, obviously wants to continue to live simply and humbly.
"As a man of prayer both qualities will bring a different style of leadership to the papacy, and inject a much-needed spirituality to the Catholic Church in the modern world."
The Archbishop of Wales, the Most Rev Dr Barry Morgan, said: "We welcome and assure Pope Francis of our prayers and our best wishes for his future ministry.
"We hope he will bring an ecumenical perspective to the role, a desire to work with Christians of all traditions and a goodwill to people of all faiths."
His Grace Bishop Angaelos, General Bishop of the Coptic Orthodox Church in the United Kingdom said: "I express my heartfelt joy shared with our Catholic brethren around the world on the appointment of Pope Francis.
"We pray God's joy and blessing upon our sister Catholic Church as it embraces its new father and shepherd, and we also pray for His Holiness as he commences this sacred ministry, strengthened and overshadowed by the grace of God."