Black smoke has appeared from the chimney of the Sistine Chapel, indicating Roman Catholic cardinals have not yet elected a new pope.
All eyes are on the chimney leading from the Sistine Chapel
The smoke came after a morning session of voting, on the second day of the process known as a conclave.
The 115 cardinals are shut off from the outside until they choose a successor to John Paul II, who died on 2 April.
Up to four ballots are held each day, and the ballot papers are burned in a stove after every second vote.
Chemicals are added to colour the smoke - black smoke signals failure to agree on a candidate, while white smoke means a new pope has been chosen.
This time the white smoke will be accompanied by the ringing of the bells of St Peter's Basilica.
Onlookers initially celebrated, thinking they had seen white smoke
The black smoke appeared just before noon (1000 GMT) after a morning session of two votes.
The BBC's Peter Gould in Rome reports there was some confusion among those gathered in St Peter's Square, as the smoke at first appeared white or light grey.
Then, as the bells of the Basilica began chiming at noon, more smoke started to emerge from the chimney, leading many people to think that a Pope had been elected. After a couple of minutes of total confusion, the smoke gradually turned black.
Further smoke - either black or white - is expected at 1900 (1700 GMT). But, if a new pope is elected in the first vote of the afternoon session, the white smoke could come earlier.
115 cardinals take part
Two other eligible cardinals are too ill to attend
Must be aged under 80
Come from 52 countries
58 from Europe
Italy (20) and US (11)
0730: Cardinals celebrate Mass in hotel
0900: Morning voting starts
1600: Afternoon voting starts
1200 & 1900: Ballot papers burned, generating smoke
All times local (GMT+2)
The cardinals re-entered the Sistine Chapel on Tuesday morning after beginning conclave on Monday. They spent the night in a hotel within the Vatican's walls.
Black smoke appeared on Monday evening, although it had not been certain that the cardinals would even hold a ballot on the first day of the conclave.
Experts had predicted that even if they did so the chance of a pope being elected on the first ballot was extremely remote.
Strict security measures have been imposed to ensure the secrecy of the conclave is kept.
Parts of the Vatican have been sealed off, and all staff who will come into contact with the cardinals have taken a vow not to divulge anything of what they see or hear.
Mobile phones, newspapers and television are banned, and the Sistine Chapel has been swept to check for bugging devices.