An estimated 300,000 people packed St. Peter's Square at the Vatican today to see Pope Francis deliver his first prayer address from a window of the papal apartment.

Before the Angelus, the new Pope made an impromptu appearance outside, prompting cheers of "Francesco" from the crowd.

In a surprise move, he shook hands with visitors as they left St. Anna's church in Vatican City, where he had celebrated mass. He kissed the foreheads of children leaving the chapel.

Many kissed the pontiff's hand, and he accepted a kiss on the cheek from one woman who had attended the service. He spoke to several people, asking some to "pray for me." He later asked for prayers on his Twitter feed.

Pope Francis is surrounded by security officials as he conducts a walkabout near a Vatican gate.

"This is what he was known for as he was cardinal in Argentina, getting amongst the people," Vatican analyst David Perlich told CBC News. "So I am sure this is setting the stage for what we can expect for years to come."

"This Pope is like listening to a parish priest. He has such a casual presence," Perlich said.

Before the mass, Francis went over to the chief of his security detail and indicated that he wanted to greet two priests in the crowd, who approached and embraced him.

In his homily, Francis spoke only five minutes, saying the core message is "that of mercy." He said God has an unfathomable capacity to pardon, and noted that people are often harder on each other than God is toward sinners.

As he later appeared to the faithful from his studio window overlooking St. Peter's Square, he spoke again about God's power to forgive.

"He doesn't tire of forgiving us if we return to him with a contrite heart," the Pope told the crowd.

"Afterwards when I spoke to people, they expressed how they believed that this Pope will change the temperature of the church, the tone, that he's more accessible and he speaks off-the-cuff, and goes off the text. He makes jokes, we saw that yesterday and today," said CBC's Susan Ormiston, reporting from the Vatican.

"So they're feeling that this is a very approachable Pope."

"He's brutally honest. He's someone who speaks his mind. He's someone who speaks in a very clear way, so I think the fact he's a clear, articulate spokesman for the faith, that's what people and the cardinals want to see in their pontiff," Dr. Peter Baltutis, an instructor in Christianity and culture at the University of Toronto, told CBC News.

Francis was elected Pope last Wednesday and will be formally installed this Tuesday. He is the first Latin American pope and the first Jesuit pope in modern times.

Dignitaries from around the world attended Sunday's ceremony in St. Peter's Basilica.

Canada will be represented at Tuesday's ceremony by Gov. Gen. David Johnston.

With files from The Associated Press