Pope Benedict XVI has called on the Catholic Church and its faithful to "renew" and "refocus on God by disowning pride and egoism" in his penultimate Angelus prayer before he steps down.

Thousands had gathered in St Peter's Square for Benedict XVI's first Sunday window blessing since his retirement announcement, and the second-to-last before he leaves the papacy.

The meditation service in Vatican City marked the beginning of the traditional Lenten period of reflection and prayer.

"The Church calls on all its members to renew themselves ... which constitutes a fight, a spiritual battle, because the evil spirit wants us to deviate from the road towards God," Benedict, 85, said from his balcony.

The traditional noon appointment normally attracts a few thousand pilgrims and tourists, but city officials had expected as many as 150,000 people to flock to the cobblestone square for one of their last chances to see Benedict before he relinquishes his stewardship of the Roman Catholic church and its nearly 1.2 billion members.

From Sunday evening, Benedict will be out of the public eye for an entire week.

Rome threw on extra buses and subway trains to help deal with the expected crush of people, and offered free shuttle vans for the elderly and disabled.

Benedict shocked the world last week by announcing he is resigning on February 28 - the first papal abdication in 600 years.

Conclave date

While cardinals elect Benedict's successor next month in a secret conclave in the Sistine Chapel, he will be in retreat at the Holy See's summer estate in the hills southeast of Rome.

After several weeks, he is expected to move into a monastery being refurbished for him behind Vatican City's walls and lead a largely cloistered life.

The Vatican has not announced the date of the start of the conclave, but said on Saturday that it might start sooner than March 15, the earliest date it can be launched under current rules.

Al Jazeera's Simon McGregor-Wood explains how
Pope Benedict XVI announced his retirement

Benedict would have to sign off on any earlier date, an act that would be one of the last of his nearly eight-year papacy.

Meanwhile, the first cardinals started arriving in Rome to begin a period of intense politicking among the "princes of the church" to decide who are the leading candidates to be the next pope.

Guinea-born Archbishop Robert Sarah, a cardinal who leads the Vatican's charity office, said when he arrived on Sunday at Rome's airport that the churchmen should select their new leader with "serenity and trust".

The Vatican has raised the possibility that the conclave to elect the next pope might start sooner than March 15, the earliest date possible under current rules that require a 15 to 20 day waiting period after the papacy becomes vacant.

Vatican spokesman the Rev Federico Lombardi said on Saturday that Vatican rules on papal succession were open to interpretation and that "this is a question that people are discussing".

"It is possible that church authorities can prepare a proposal to be taken up by the cardinals on the first day after the papal vacancy" to move up the start of the conclave, he said.