The Obamas and Bidens shook hands with the Argentine-born pontiff as he made his way down a receiving line and was welcomed by young schoolchildren and warm cheers of "Hello, hey, hey, welcome to the USA."

Presidents rarely welcome foreign leaders at the airport, although President George W. Bush set a precedent when he met Pope Benedict XVI at Andrews in 2008.

Francis, 78, was whisked away in a small black Fiat 500L, headed for the Apostolic Nunciature, the Vatican's diplomatic mission in northwest Washington, where scores of people waved Argentine flags from behind a barricade.

He greeted some of them briefly outside the nunciature before ducking inside.

The six-day visit is marking the popular and unpredictable pope's first time in the United States and includes a packed schedule through Washington, New York and Philadelphia. There are also unprecedented security measures in each city as throngs of Catholic faithful travel to see him.

Francis arrived from Cuba, where he held his first papal Mass in the region in front of thousands and had an audience with President Raul Castro and Fidel Castro.

The pope's trip begins in earnest Wednesday morning with a ceremony on the White House South Lawn. On Thursday, he'll address a joint session of Congress and then fly to New York. On Friday, he will speak at the United Nations and celebrate Mass at Madison Square Garden.

On Saturday and Sunday, he will be in Philadelphia for World Meeting of the Families, a conference billed as the largest gathering of Catholic families.

Source: nbcnews.com