Pope Francis said an open-air Mass before a huge crowd on Sunday to wrap up a jamboree of Catholic youth, the last big event before he returns to Rome to prepare for a historic trip to the Arabian Peninsula in one week.

Organisers said about 700,000 people attended the closing mass of World Youth Day, which takes place in a different city every three years. The next jamboree, which has been dubbed the 'Catholic Woodstock', will be in Lisbon, Portugal, in 2022.

Many of the young people in the crowd spent the night on the fields of a park named after Pope John Paul, who was the last pontiff to visit Panama, in 1983.

In his closing homily at the mass, which started unusually early at 8 am, because of the sweltering tropical heat, Francis urged the young people to work against 'fear and exclusion, speculation and manipulation'.

After a week at the Vatican, Francis leaves on Sunday for a three-day trip to Abu Dhabi in the United Arab Emirates, where he will become the first pope to visit the Arabian Peninsula and say the first mass in a public venue there. There are about 1 million Roman Catholics in the UAE, all of them expatriate workers.

The freedom to practise Christianity – or any religion other than Islam – is not a given in the Gulf and varies from country to country. In the UAE and Kuwait, Christians may worship in churches or church compounds and in other places with special licences. Saudi Arabia, home to Islam's holiest sites, bans the practice of other religions.

During the Panama trip, the themes of migration and the Church's sexual abuse crisis loomed large.

Francis said at one event that it was 'senseless and irresponsible' to stigmatise migrants and see all of them as threats to society, weighing in again on one of the most divisive issues in the United States.

He spoke several times of the need for 'bridges, not walls', again putting himself at odds with US President Donald Trump, who on Friday agreed under mounting pressure to end a 35-day partial US government shutdown but without getting the $5.7 billion he had demanded from Congress for a wall along the US-Mexico border.

Trump has repeatedly warned about the dangers of illegal immigrants, and said the wall would help solve the problem.

On Saturday, Francis said the Roman Catholic Church was weary and 'wounded by her own sin', in an apparent reference to the global sexual abuse crisis.

Later, at a lunch with a delegation of young people, he told the American representative that clergy sexual abuse was a 'horrible crime' and that the Church should be united in fighting it.

Francis has called a summit of the heads of national Catholic churches at the Vatican February 21-24 to discuss what is now a global sexual abuse crisis.

The February meeting offers a chance for him to respond to criticism from victims of abuse that he has stumbled in his handling of the crisis and has not done enough to make bishops accountable.