VATICAN CITY, Holy See (AFP) — Firefighters at the Vatican installed a chimney on top of the Sistine Chapel to be used during the conclave that begins 7 May, an Agence France-Presse reporter witnessed Friday.

Cardinals vote in secret in the chapel for a new pope and reveal to the waiting world the outcome by burning the ballots in a special stove, with the chimney emitting black smoke if no one has been elected, or white smoke if there is a new pope.

Cardinals from around the world have been called back to Rome following the death of Pope Francis, the Argentine who led the Catholic Church for 12 years until his death on 21 April aged 88.

The 133 cardinals who are under 80 years old and therefore eligible to elect his successor will begin voting in secret, in a process expected to take several days.

On the first day they vote once, and during the following days they hold two votes in the morning and two in the afternoon.

If a candidate secures the two-thirds majority required to win — at least 89 votes — then the ballots will be burned in the special stove with the addition of chemicals to emit a white smoke.

If no candidate has enough votes during the first morning vote, the cardinals will proceed to a second vote, and only after that point will the ballots be burned.

If no pope is elected, no chemicals are added and the smoke that comes out of the chimney is black.

The afternoon session follows the same procedure — if a pope is elected in the first vote, there will be white smoke, but if not, the cardinals will proceed to a second vote and only after that will the ballots be burned.