Watch: Cardinals enter conclave to decide who follows Pope Francis

Roman Catholic cardinals have begun the task of electing a new pope, locking themselves away from the world until they choose the man they hope can unite a diverse but divided global Church.

In a ritual dating back to medieval times, the cardinals filed into the Vatican's frescoed Sistine Chapel after a public Mass in St Peter's Basilica and started their secret conclave for a successor to Pope Francis, who died last month.

No pope has been elected on the first day of a conclave for centuries, so voting could continue for several days before one of the cardinals receives the necessary two-thirds majority to become the 267th pontiff.

There was only one ballot on Wednesday, with black smoke being released from the newly constructed chimney that night. Thereafter, the cardinals can vote as many as four times a day.