Pope Francis has arrived in the City of Brotherly Love for the final leg of his US visit - a festive weekend devoted to celebrating Catholic families.

The pontiff's plane touched down at the Philadelphia airport after take-off from New York, bringing him to a city of blocked-off streets and checkpoints manned by police, National Guardsmen and border agents.

After speeches to Congress and the United Nations earlier this week aimed at spurring world leaders toward bold action on immigration and the environment, he is expected to focus more heavily on ordinary Catholics during his two days in Philadelphia.

On the itinerary for today - a visit to the Cathedral Basilica of Sts. Peter and Paul for a Mass for about 1,200 people, and a late-afternoon speech in front of Independence Hall on religious freedom and immigration. The weekend's events will culminate in an outdoor Mass on Sunday evening for one million people.

Among those greeting Pope Francis at the airport was Richard Bowes, a former Philadelphia police officer wounded in the line of duty seven years ago. Pope Francis also got out of his black Fiat to bless a man in a wheelchair on the tarmac, kissing him on the forehead.

A Catholic high school band played the theme song from the Philadelphia-set movie Rocky.

On the first two legs of his six-day US journey, in Washington and New York, Pope Francis was greeted by throngs of cheering, weeping well-wishers hoping for a glance or a touch from the wildly popular spiritual leader, despite unprecedented security.

The Philadelphia visit, months in the making, all but paralysed Center City, with stretches of Broad and Market Streets and other routes closed to all but pedestrians and lined with metal crowd-control barricades, massive concrete blocks and tall fences.

"He has a magnetic personality that not only appeals to Catholics, but to the universal masses. He's not scripted. He's relatable. His heart, in itself, you can see that reflected through his message," said Filipina Opena, 46, a Catholic from LaMirada, California, as tour groups and families walked among Philadelphia's historic sites ahead of the pope's visit. "People feel he's sincere and he's genuine."

In Philadelphia, Pope Francis will be the star attraction at the World Meeting of Families, a conference for more than 18,000 people from around the world.

An Argentine on the first US visit of his life, the 78-year-old Pope Francis will be given a stage steeped in American history. Independence Hall was where the Founding Fathers signed the Declaration of Independence and Constitution. Francis was scheduled to speak from the lectern Abraham Lincoln used to deliver the Gettysburg Address.

As he has done in New York and Washington, the pontiff will give his attention to both the elite and the disadvantaged, this time visiting inmates in Philadelphia's largest jail.

Tonight, on Benjamin Franklin Parkway, the cultural heart of the city, he will be serenaded by Aretha Franklin and other performers at a festival celebrating families. He will return there tomorrow for the Mass, his last major event before leaving that night for Rome.

"It's probably not politicians who will remember his message but the kids," said Liza Stephens, 48, of Sacramento, California, who was in Philadelphia with her two daughters, aged 10 and 12. The three spent time volunteering to bag food for Africa, among other activities at the family conference.

The Archdiocese of Philadelphia organised the conference, hoping for a badly needed infusion of papal joy and enthusiasm amid shrinking membership, financial troubles and one of the worst clergy sex-abuse scandals to hit a US diocese.

The archdiocese has been the target of three grand jury investigations. The last grand jury accused the diocese in 2011, before Archbishop Charles Chaput came to Philadelphia, of keeping on assignment more than three dozen priests facing serious abuse accusations.

A monsignor who oversaw priest assignments was found guilty of child endangerment, becoming the first American church official convicted of a crime for failing to stop abusers.

The pope is widely expected to talk privately with abuse victims this weekend.