Cardinals are now behind the sealed doors of the Sistine Chapel at the Vatican, where they will remain until a new pope is elected.

American Cardinals walk to a bus to take them from the North American College to St. Peter's Basilica (Joe Raedle/Getty Images)

At a Mass before the process began, they heard a final appeal for unity amid divisions and uncertainty over who will lead the 1.2 billion-strong Catholic Church and tend to its many problems.

The cardinals held their final closed-door debate Monday over whether the church needs more of a manager to clean up the Vatican's bureaucratic mess or a pastor to inspire the 1.2 billion faithful in times of crisis. Not all cardinals had a chance to speak, suggesting there's still unfinished business going into the first round of voting.

There is no clear front-runner and no sense that a single man has what it takes to fix the church's many problems.

However, speculation has begun to focus on Italian Cardinal Angelo Scola and Brazilian Cardinal Odilo Scherer. Scola is as favored by cardinals hoping to shake up the Vatican bureaucracy. Scherer is a favorite of Vatican-based insiders who want to maintain the status quo.

Cardinals enter the Sistine Chapel on Tuesday, and there's no indication how long voting will last.

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