Crowds of faithful in St Peter's Square cheered and the bells of St. Peter's Basilica tolled in a further sign that the 133 cardinals, including four from Poland, chose a successor to Pope Francis, who died last month.
The election came on the first full day of voting by the cardinal electors, who secluded themselves behind the chapel's closed doors on Wednesday afternoon, the Reuters news agency reported.
The identity of the new pontiff and the name he has chosen were expected to be announced shortly.
Ahead of the conclave, some cardinals said that a swift election of the new pope would signal unity after the often-divisive 12-year papacy of Francis, according to reports.
Francis, who was elected in 2013 following the resignation of Pope Benedict XVI, died on April 21 at the age of 88.
He was the first pontiff from the Americas and the first Jesuit pope.
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Source: IAR, PAP, TVP Info, Reuters