Pope Benedict XVI was spending his last night in his Vatican apartments Thursday after bidding an emotional farewell to 150,000 pilgrims in St Peter's Square on the eve of his historic resignation.

The German pontiff was greeted with whoops, chants and cheers. Huge banners carried messages such as "Benedict, we'll miss you!" and "The pope is the heart of this city!"

In his speech, the 85-year-old spoke of "stormy waters" in an apparent reference to the multiple scandals that have plagued his reign, and said he had decided to resign for the good of the Roman Catholic Church.

"The Lord gave us days of sun and of light breeze, days in which the fishing was good," said the head of the world's 1.2 billion Catholics.

"There were also moments when there were stormy waters and headwinds... as if God was sleeping.

"But I always knew that God was in that boat and I always knew that the boat of the Church is not mine, is not ours, but is his and he will not let it sink," he said, adding: "I never felt alone."

The former Joseph Ratzinger stunned the world with his abrupt decision to end an eight-year reign dogged by scandal and Vatican infighting, declaring he was too weak to keep up with the modern world.

The scourge of paedophile priests and cover-ups by their superiors and a longstanding money-laundering scandal at the Vatican bank, which exposed infighting among Benedict's closest allies, cast a shadow over his papacy.

What observers said may have been the last straw was the "Vatileaks" scandal, in which his trusted butler leaked secret papal memos revealing intrigues between rival groups of cardinals.

Wednesday's crowds however did not dwell on the scandals.

'Resigning a powerful message'

"I have come in gratitude for everything he has done these past eight years," said Father Giulio, a 67-year-old priest from Italy's Abruzzo region.

"Resigning is a powerful message for every Christian. He resigned without bitterness but instead in sweetness and serenity," he said.

Benedict is the first pope to resign of his own free will since the Middle Ages.

While the move has worried conservatives, it has kindled the hopes of Catholics around the world who want a successor to breathe new life into the Church.

"I admire Benedict, but I hope the next pope will have the strength to unite the Church and help it grow again -- and bring back a bit of morality," said Sharon Clark, a tourist from the United States.

US Secretary of State John Kerry, himself a Catholic, wished Pope Benedict XVI well on the eve of his departure.

"The United States sends its best wishes to His Holiness Pope Benedict XVI as he leaves the Vatican after years of service and dedication to God, the Catholic Church, and world peace," said Kerry in statement.

The Vatican has said Benedict will receive the title of "Roman pontiff emeritus", can still be addressed as "Your Holiness" and will wear the white papal cassock after he officially steps down at 1900 GMT on Thursday.

Benedict will spend the first few weeks of his retirement at the summer papal residence of Castel Gandolfo outside Rome.

There he will be well away from the preparations and consultations ahead of next month's secret conclave to elect his successor, but in due time he will return to the Vatican to take up residence there.

Rome has been gripped by speculation over who the leading candidates might be to replace him -- the so-called "papabili" -- as cardinals from around the world fly in ahead of the conclave.

Rumours and counter-rumours in the Italian media suggest cloak-and-dagger lobbying, prompting the Vatican to condemn what it has called "unacceptable pressure" to influence the papal election.

One of them, Cardinal Juan Luis Cipriani of Peru, said he was confident they would elect a new pope before Holy Week, the event-laden run-up to Easter, Christendom's most important observance, on March 31.

"The coordination meetings have not begun and no decision has yet been made on when the conclave will be held, but I clearly expect that before Holy Week we will have among us a new holy father," he said.