Cardinals from five continents held a final mass in St Peter's Basilica in the Vatican on Wednesday before sealing themselves away to elect a new pope to lead the world's 1.4 billion Catholics.

A total of 133 cardinal electors are expected to take part in the conclave, the voting process to pick a successor to Pope Francis, who died last month after a 12-year papacy.

No clear frontrunner has emerged from among the prelates, representing a range of progressive and conservative traditions within the Church, and the contest to lead the 2,000-year-old institution appears wide open.

In a time of geopolitical uncertainty, the new pope faces diplomatic balancing acts, as well as Church infighting, the continued fall-out from the clerical child abuse scandal, and, in the West, increasingly empty pews.

The "Princes of the Church" began a pre-conclave mass in St Peter's Basilica at 10am (0800 GMT), presided over by the dean of the College of Cardinals, Giovanni Battista Re.