By Joshua McElwee, Crispian Balmer and Philip Pullella
VATICAN CITY (Reuters) - Black smoke billowed from a chimney atop the Sistine Chapel on Thursday, signalling that the cardinals locked in a conclave have not yet chosen a new pope to guide the Roman Catholic Church.
Thousands of faithful gathered in St. Peter's Square waited for smoke to pour from the flue on the chapel's roof, which it did shortly before noon (1000 GMT).
The 133 cardinals under the age of 80 began the heavily ritualised and secret process on Wednesday, shut away in complete isolation as they pick a successor to the late Pope Francis.
They burn the ballot papers and mix them with chemicals to show how proceedings are going -- black signalling no pope and white announcing a new pontiff.
The cardinals held an initial inconclusive vote on Wednesday evening. They are scheduled to hold up to two more ballots on Thursday afternoon, with possible smoke signals expected some time after 5:30 p.m. (1530 GMT).
The red-hatted "princes of the Church" will keep on voting up to four times a day until someone wins a two-thirds majority.
No pope in modern times has been elected on the first attempt, so Wednesday's black smoke was widely expected. But given recent history, a final result is possible from the second day.
Francis, the first pope from Latin America, was elected on the evening of the second day of the last conclave, held in 2013, as was his predecessor, Benedict XVI, in 2005.
(Reporting by Joshua McElwee, Crispian Balmer, Philip Pullella and Alvise Armellini; Editing by Nia Williams and Frances Kerry)
