Prevost is 1st American Pope and will be known as Leo XIV

Robert Francis Prevost became the first pope from the United States on Thursday, picking the papal name Leo XIV after cardinals from around the world elected him leader of the world's 1.4 billion Catholics.

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Tens of thousands of people packed in St Peter's Square cheered as Prevost appeared on the balcony of St Peter's Basilica, waving with both hands, smiling and bowing.

"Peace by with you," he told the crowds.

White smoke from the Sistine Chapel had billowed into the sky on the cardinals' second day of voting to announce his election in a secret conclave, while the bells of St Peter's Basilica and churches across Rome rang out.

Crowds of people rushed towards the square to watch the balcony of the basilica, which has been fitted out with red curtains for the first address to the world by the 267th pope.

The new pontiff, who succeeds Argentine reformer Pope Francis, was introduced in Latin with his chosen papal name.

"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 reporters as people around him jumped up and down in excitement.

There were euphoric scenes as one priest sat on someone's shoulders waving a Brazilian flag and another lifted a heavy crucifix into the air in jubilation.