Pope Leo XIV will celebrate mass Friday, the day after becoming the first US head of the Catholic Church, with the world watching for signs of what kind of pope he will be. Chicago-born Robert Francis Prevost was on Thursday elected by fellow cardinals to lead the world's 1.4 billion Catholics after a secret conclave in the Vatican's Sistine Chapel. At 11:00 am (0900 GMT) Friday, the 69-year-old will return to the chapel to celebrate a private mass with cardinals that will be broadcast by the Vatican, delivering his much anticipated first homily as pope. Tens of thousands of well-wishers cheered Leo as he appeared on the balcony of St Peter's Basilica on Thursday evening -- but many did not know who he was. The American, who spent two decades doing missionary work in Peru and was only made a cardinal in 2023, had been on many Vatican watchers' lists of potential popes although he is far from being a globally recognised figure. Over the coming days, from Friday's mass to Sunday's midday Regina Coeli prayer and a meeting with journalists at the Vatican on Monday morning, his actions and words will be closely scrutinised. - Build bridges - In his first speech to the crowds packed into St Peter's Square on Thursday evening, Leo echoed his predecessor Pope Francis with a call for peace. "Help us, and each other, to build bridges through dialogue, through encounter, to come together as one people, always in peace," he said. "We must seek together how to be a missionary Church, a Church that builds bridges, which holds dialogues, which is always open." World leaders raced to welcome his election as the 267th pope and promised to work with the Church on global issues at a time of great geopolitical uncertainty. Leo faces a momentous task. As well as asserting his moral voice on a conflict-torn world stage, he must try to unite a divided Church and tackle burning issues such as the continued fallout from the sexual abuse scandal. As Cardinal Prevost, the new pope had defended the poor and underprivileged and had reposted articles online critical of US President Donald Trump's anti-migrant policies. But Trump nevertheless welcomed his election, saying on Thursday it was a "great honour" to have a pope from the United States. It was not known how many ballots it took to elect Leo XIV, but the conclave followed recent history in wrapping up in less than two days. - Consensus candidate - The crowds erupted with cheers on Thursday when white smoke billowed into the sky from the Sistine Chapel chimney, the traditional sign that a new pope has been elected. "It's an amazing feeling," said an elated Joseph Brian, a 39-year-old chef from Belfast in Northern Ireland, who came with his mother to Rome for the spectacle. "I'm not an overly religious person but, being here with all these people just blew me away," he told AFP as people around him jumped up and down in excitement. With the choice of Prevost, experts said, the cardinals had opted for continuity with the late Francis, a progressive from Argentina who shook up the Church in his 12-year papacy. "He is a moderate consensus candidate who fits into a soft continuity, a gentle continuity with Pope Francis, who will not alienate conservatives," said Francois Mabille, a researcher at the Paris-based think tank IRIS and author of a book on Vatican strategy. "At least, he has not alienated them." But Mabille predicted a more cautious style than Francis, whose declarations sometimes caught even fellow senior churchmen off guard. "It is a posthumous success for Pope Francis, with undoubtedly some different accents and embodiment of the pontifical role," he said. "I do not think we will find in him the sometimes divisive statements Francis had or equally virulent criticisms of liberalism."