ROME (CNN) -- Amid pomp and ceremony, Benedict XVI left Vatican City Thursday for the last time as pope, ahead of his historic resignation as leader of the world's 1.2 billion Catholics.
An honor guard of Swiss Guards, the soldiers who traditionally protect the pope, lined up to bid him farewell as he left the papal apartment, alongside senior Vatican officials and staff.
Applause swelled as Benedict, looking frail and carrying a cane, climbed into a car that took him to the helicopter that flew him to the summer papal residence, Castel Gandolfo.
The sound of bells from St. Peter's Basilica chimed across the city of Rome as the helicopter soared overhead, passing above landmarks like the Colosseum.
At 8 p.m. (2 p.m. ET), his almost unprecedented resignation takes effect.
Although Benedict will eventually return to Vatican City to live out his days, he will never again set foot there as pope.
His final tweet, sent at 11 a.m. ET from his @Pontifex account, read: "Thank you for your love and support. May you always experience the joy that comes from putting Christ at the centre of your lives."
Some 10,000 people, some local residents, had gathered to greet Benedict in the village of Castel Gandolfo amid a festive, party atmosphere.
On landing nearby, he was given a formal welcome by local dignitaries and Vatican officials.
Benedict will make one last public appearance on the Castel Gandolfo balcony to bless the crowds before retreating into seclusion.
It may be the last time he is seen in public.
At 8 p.m., the Swiss Guards will ceremonially leave the gates of the residence and seals will be placed on entrance to the pope's Vatican apartment, the Vatican said.
The pope has the right to wear the symbolic Fisherman's Ring until 8 p.m., Lombardi said.
After that the ring and Benedict's papal seal will be "destroyed" by means of making scratch marks so that they can no longer be used to seal documents, he added.
The process of transition to a new pope will then begin.
Benedict, who will be known as "pontiff emeritus," will spend the next few weeks at the residence before moving to a small monastery within the Vatican grounds.
He entered his final day as pontiff with an unusual act -- a pledge of "unconditional obedience" and respect to whoever takes up the reins after his dramatic resignation later.
His promise came in a last meeting Thursday morning with the cardinals who will pick his successor, almost certainly from within their own ranks.
"I will continue to serve you in prayer, in particular in the coming days," he said, as they work to elect the new pope.
His words appeared designed to answer concerns that the presence of a former pontiff might lead to confusion or competing loyalties once the new pope is installed.
Benedict told the cardinals it was a "joy to walk with you" during his nearly eight tumultuous years at the head of 1.2 billion Catholics worldwide.
Vatican spokesman the Rev. Thomas Roscia said he believed 144 cardinals had attended Benedict XVI's farewell to them as pope. That includes both cardinal-electors, who are under the age of 80, and cardinals who are not eligible to vote for the next pope.
Not all the 115 cardinals eligible to vote were present, said another Vatican spokesman, the Rev. Federico Lombardi.
Two cardinals are suffering ill health, making their attendance uncertain, although arrangements may be made to enable them to vote, Roscia said.
The new pope is almost certain to come from within the cardinals' ranks.
In their meeting Thursday morning, the cardinals gave Benedict a standing ovation, and then one by one each met the pope to say a final few words.
Cardinal Roger Mahony, the retired archbishop of Los Angeles, tweeted after the event that he had asked the pope to pray for the people of Los Angeles.
"He grasped my hand and said 'Yes'!!" Mahony said.
The current Catholic archbishop in Los Angeles earlier this month disciplined Mahony for his mishandling of "painful and brutal" allegations of sexual abuse by priests. Mahony's decision to travel to Rome to take part in the election of the new pope has been controversial because of that.
The Vatican has said it wants to have the next pontiff in place in time for the week of services leading up to Easter Sunday on March 31.
A series of meetings to set the timetable for the conclave -- the secret election of the new pope -- will begin as of next week and the cardinals need to prepare, said Lombardi.
They will receive the formal invitation to attend on Friday, he said.
Cardinal Gianfranco Ravasi of Italy, tipped as a possible future pope, tweeted Thursday morning that he would be away for a few days.
A number of other cardinals, including Ghanaian Peter Turkson, also considered a frontrunner, and New York's Timothy Dolan are also present on Twitter.
Cardinals are forbidden to communicate with the outside world -- now including by Twitter -- during the conclave, held within the Sistine Chapel.
The Vatican declined to say whether BlackBerrys, iPhones and laptops would be taken away from cardinals when they are in the conclave. There is no Internet access inside Santa Marta, where the cardinals will stay during the conclave, Lombardi said.
The @Pontifex account will go dormant Thursday until the next pope decides whether he wants to use it, Lombardi said.
Benedict, who will not be involved in the election, will not get any advance notice of who his successor will be, Roscia said. The pope emeritus will find out who has been elected at the same time as the rest of the world.
Cardinal Javier Lozano Barragan of Mexico, who turned 80 last month and so is not a cardinal-elector, would not be drawn to comment Wednesday on who the next pope might be.
As to whether the cardinals are talking to each other about it now, he told CNN: "There are contacts, of course there are contacts. But what people talk about, who knows?
"There is a saying in Rome: He who enters the conclave as a possible pope comes out a cardinal."
Mired in scandal
Benedict's resignation opens up the prospect of unforeseen opportunities and challenges for the Roman Catholic Church.
Many are wondering whether a new pontiff will choose to lead the church in a different direction -- and can lift it out of the mire of scandal that has bogged down this pope's time in office.
Even as Benedict's final week began, Vatican officials were trying to swat down unsavory claims by Italian publications of an episode involving gay priests, male prostitutes and blackmail. Then the news broke that Benedict had moved up the resignation of a Scottish archbishop linked over the weekend by a British newspaper to inappropriate relationships with priests.
Last year, leaks of secret documents from the pope's private apartment -- which revealed claims of corruption within the Vatican -- prompted a high-profile trial of his butler and a behind-doors investigation by three cardinals.
Their report, its contents known so far only to Benedict, will be handed to his successor to deal with, the Vatican said.
Vatican magistrates may have authorized the tapping of two or three telephone lines during the cardinals' inquiry into the leaks, Lombardi acknowledged Thursday.
He was responding to a report in the Italian weekly magazine Panorama claiming that there had been a large-scale wiretapping and surveillance operation during the investigation.
Lombardi denied there had been "a massive" operation on the scale reported by the magazine," saying there is "no foundation" for the article. Roscia said that if there was any wiretapping or surveillance, "it's a very small process."
Both spokesmen denied that the operation had been ordered by the three cardinals, saying that if it had happened, it was ordered by magistrates.
At the same time, the church faces continued anger about what many see as its failure to deal with child sex abuse by priests.
So, when Benedict announced on February 11 that he would step down, becoming the first living pope to resign in 598 years, there was inevitable speculation that his move was in some way linked to the brewing scandals.
Dolan, the most senior Catholic cleric in the United States, told CNN's Christiane Amanpour that the new pope wouldn't seek to alter the teachings of the church, but could change the way they are presented.
There is an urgent need for a recovery and renewal in the church, Dolan said.
'The Lord seemed to sleep'
The danger for the Vatican is that the scandals risk overshadowing what others see as Benedict's real legacy to the church: his teaching and writings, including three papal encyclicals.
Proof of the Vatican's irritation came with a stinging statement Saturday complaining of "unverified, unverifiable or completely false news stories," even suggesting the media is trying to influence the election of the next pope.
The constant buffeting by scandal will doubtless also have taken a toll on an 85-year-old man whose interests lie in scholarly study and prayer rather than damage control.
Benedict suggested as much at his final general audience Wednesday, when in front of cheering crowds in St. Peter's Square he spoke of steering the church through sometimes choppy waters.
There had been "many days of sunshine," he said, but also "times when the water was rough ... and the Lord seemed to sleep."
The pope also called for a renewal of faith, and for the prayers of Catholics around the world both for him and his successor.
Italian iReporter Giovanni Francia was in St. Peter's Square to witness the scene. "There was a good atmosphere, (but) full of the sense we have lost a sort of 'grandfather,'" he said. "Now we are a little more alone."
Although his departure leaves the church facing many questions, Benedict suggested that its future, "at a time when many speak of its decline," lies in seeing it as a community of many people united in a love of Christ, rather than as an organization.
CNN's Richard Allen Greene reported from Rome and Laura Smith-Spark reported and wrote from London. Hada Messia also contributed from Rome, Barbie Latza Nadeau from Castel Gandolfo and Sarah Brown from London.