POPE Francis' final mass in Dublin today drew far fewer well-wishers than expected due to torrential rain.

More than 500,000 tickets were available for the outdoor sermon in Phoenix Park - but only around 130,000 pilgrims braved the weather, aerial photographs show.

His Holiness' sermon drew far fewer people than the historical visit of Pope John Paul II to the same park in 1979, which attracted 1.25 million people.

The Vatican has not yet made any comment on the embarrassingly low turnout figure, which has been estimated from information gathered by officers overseeing the event.

Organisers had expected the crowds to trump that of Pope Francis' predecessor - but arial photos show gaps in the audience and lots of spare space in the park.

Despite the bad weather and low turnout, Pope Francis appeared in high spirits after he begged for God's forgiveness over the abuse scandal in Ireland.

In a long prayer to the assembled pilgrims at Phoenix Park, the 81-year-old asked for forgiveness for the abuse and mistreatment that had been inflicted by figures within the Church.

Earlier today the Pope said everyone would be moved by the heartbreaking stories of abuse which robbed young victims "of their innocence".

Thousands who came to see the Pope at the Marian Shrine - revered by Irish Catholics - in Knock earlier in his visit had applauded as he urged decisive steps to bring truth to the victims.

The pontiff's trip is the first papal visit to the predominantly Catholic Republic of Ireland since 1979.

He said this morning: "This open wound challenges us to be firm and decisive in the pursuit of truth and justice.

"I beg the Lord's forgiveness for these sins and for the scandal and betrayal felt by so many others in God's family.

"I ask our Blessed Mother to intercede for the healing of the survivors and to confirm every member of our Christian family in the resolve never again to permit these situations to occur."

Only 130,000 people snapped up tickets to see Pope Francis at the outdoor mass on the last day of his visit.

Francis spent 90 minutes on the first day of his two day visit to meet privately with eight victims of sexual abuse.

Some of the survivors who attended the behind-closed-doors meeting said the pontiff employed blunter language with them, apparently using the Spanish word "caca" - Spanish for "shit" - to describe those who covered up abuse.

One of them, Clodagh Malone, said Francis was "shocked" at what they told him and "he listened to each and every one of us with respect and compassion."

The survivors asked Francis to speak out on Sunday to let all the mothers know that they did nothing wrong and that it wasn't a sin as church officials have told them to try to find their children later in life.

On his arrival in Dublin he immediately spoke of his "pain and shame" at the church's child abuse scandal.

The Pope's decision to address the dark legacy of abuse in a speech in Dublin Castle drew praise in some quarters.

But others criticised Francis for not offering a public apology or directly acknowledging the Vatican's role in the failures.