Latin America's first pope inaugurated his papacy on Tuesday with an address to an estimated 200,000 in St. Peter's Square in Rome, calling for the defense of the weakest in society and of the environment.
In the hours before the Mass was due to start, thousands of faithful gathered around large television screens set up in the central square of Plaza de Mayo, overlooked by the cathedral and the famous pink presidential palace.
In his telephone message at 3:30 a.m. local time, Francis, or Francisco as he is known in the Spanish-speaking world, thanked the crowds for their prayers.
"Thank you for praying, for your prayers, which I need a lot," he said. "I want to ask you a favor that we walk together, that we look after each other ... look after life, look after the family, nature," he said.
"Don't forget this bishop, who though far away, cares so much for you. Pray for me," he added, drawing cheers and applause from the crowd.
Some of the worshippers slept outside wrapped in the yellow and white flag of the Vatican. Others prayed inside the cathedral.
"We're so happy to have an Argentine pope, someone full of humility, intelligent, who cares about everyone," said housewife Mariana O'Connor, 51.
"I think this will mean a big change in the country, it will transmit peace and harmony, which is what we need in Argentina," she told Reuters Television.
Jose Maria Di Paola, a priest who works in the slums and a friend of the pope, said Francis was popular with the millions of Argentines who live in poverty.
"Lots and lots of good memories of him and how he accompanied us come to mind," he said in Plaza de Mayo. "The people in the slums love him, they feel he is one of them."
Francis, the former Cardinal Jorge Bergoglio, took his name in honor of St. Francis of Assisi, a symbol of poverty, simplicity, charity and love of nature.
Known for traveling by bus and shunning the luxuries of high Church office, Bergoglio lived in a one-room apartment next to the cathedral and grew up in a middle-class family in Buenos Aires.
(Reporting by Helen Popper and Miguel Lobianco; Editing by Eric Beech)