It was utter confusion at the beginning. Was the smoke black or white against that grey sky? Then at 6pm Italian time, bells rang and some of the crowd became excited - but the tolling was only marking the hour, writes Patsy McGarry in Rome.
Then a man was seen on a balcony near the Sistine Chapel gesturing wildly across St Peter's Basilica towards the bells. He began imitating the flailing movements of a demented bell-ringer. He was getting his message across to the other side in an old-fashioned way.
By 6.04pm the message had got through and the bells pealed out loud and long. And as they pealed, people ran in their thousands through the streets of Rome to St Peter's.
Very soon nuns, seminarians, clergy, old women, girls, men and young women with buggies carrying small children crushed into the square.
There was a cheer as the curtains over at the balcony on the centre window of St Peter's Basilica were adjusted, then jeers as they closed.
Minutes later Cardinal Jorgé Medina Estevez of Chile, the senior cardinal deacon, stepped on to the balcony.
"Is that the new Pope? Who is he? He looks old," said a woman in the crowd. The cardinal then made his announcement: "Habemus Papam" - "We have a pope".
"Oh God," the woman said on hearing the cardinal say the names "Joseph" and "Ratzinger".
He would be Benedict XVI.
"Did he say the sixth or 16th?" asked an American woman. There was shock and wild cheering as the new Pope emerged. He spoke nervously, as "a simple, humble worker in the Lord's vineyard" who was "consoled by the fact that the Lord is able to work and act with insufficient instruments and, above all, I rely on your prayers".
The went wild and waved their American, Nigerian, Spanish, Cuban, Philippines, French, Australian flags.
It began to rain lightly, but nothing could dampen the spirit.