DUBLIN - Pope Francis has said he is ashamed of the Catholic Church's failure to adequately address the "repellent crimes" of sex abuse by clergy.

The Irish prime minister earlier delivered a strong warning to the Pope to take action against clergy involved in child abuse and keeping it secret. The Pope is expected to meet abuse survivors later on Saturday.

The papal visit, the first to the Irish Republic for 39 years, coincides with the World Meeting of Families. It is a global Catholic gathering held every three years.

Irish Prime Minister Leo Varadkar on Saturday urged Pope Francis to take action to ensure justice for abuse victims worldwide.

Varadkar, an openly gay leader and a symbol of Ireland's liberalising culture, demanded from Pope Francis "that from words flow actions" for abuse victims in a strongly-worded speech.

Speaking to an audience in Dublin Castle alongside the pope, Varadkar said Ireland's multiple historic scandals were "stains on our state, our society and also the Church."

"Far too often there was judgement, severity and cruelty... people kept in dark corners, behind closed doors, cries for help that went unheard," he added.

"There is much to be done to bring about justice and truth and healing for victims and survivors. Holy Father, I ask that you use your office and influence to ensure that this is done here in Ireland and across the world." Francis responded, saying that the failure of the Church authorities "to address these repellent crimes has rightly given rise to outrage, and remains a source of pain and shame for the Catholic community.

"I myself share those sentiments," he added.

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Under cloudless skies, the pope's "Shepherd One" flight landed in Dublin at 10:26 am (0926 GMT) where he was met on the red carpet by Foreign Minister Simon Coveney and his children, who presented him with a bouquet of white and yellow roses.

It was the first time a pope had set foot in the former bastion of Catholicism since pope John Paul II spoke to a crowd of 1.5 million people during his visit in 1979.

Hundreds of thousands of wellwishers are expected to follow Francis during his two-day tour of Dublin and County Mayo in Ireland's far west.

Supporters carrying banners reading "We Heart The Pope" and "Pope Francis, Together We Love You Forever" lined the road, cheering as his motorcade passed by. "In some ways the church has gone through a lot in the last few years - it's a way the Holy Father can support us," Anne-Marie Dean, 47, from Dublin, said of the visit.

But a new generation has shed Ireland's traditional mores, electing Ireland's first openly gay prime minister and voting to legalise same-sex marriage and abortion - both once unthinkable.

During his speech, the pope broached the abortion vote, asking: "could it be that the growth of a materialistic 'throwaway culture' has in fact made us increasingly indifferent to the poor and to the most defenceless members of our human family, including the unborn?" Earlier this month, the Vatican was rocked by another abuse scandal when a devastating US report accused more than 300 priests in Pennsylvania state of abusing more than 1,000 children since the 1950s.

The pope wrote a letter to the world's 1.3 billion Catholics vowing to prevent future "atrocities" but also conceding that no efforts "to repair the harm done will ever be sufficient".

Ireland has grappled with its own history of abuse, with multiple probes finding Church leaders protected hundreds of predatory priests over the decades.

Former Irish president Mary McAleese revealed this month she challenged Vatican attempts in 2003 to keep Church documents inaccessible to government investigators.

The Argentine pontiff is in Ireland to close the 2018 World Meeting of Families (WMOF) - a global Catholic gathering that takes place every three years.

Francis will tour Dublin on Saturday on his Popemobile before visiting a hostel for homeless families and giving a speech at Croke Park stadium.

He will also meet with abuse victims during his visit.

The highlight of the trip will be an outdoor mass in the city's Phoenix Park on Sunday, which is expected to draw 500,000 people - a tenth of Ireland's population.

Priests and nuns from across Ireland have flocked to the capital, where a wide array of merchandise - from candles to dolls to t-shirts bearing the pope's image - was on sale.

Victims of clergy abuse and their supporters will hold a "Stand for Truth" demonstration in Dublin during the Sunday mass.

In Dublin, Richard Duffy, 31, said he was opposed to the visit, telling AFP "it just boggles my mind that there's a celebration for him coming here."

"They're still in denial and refusing to admit any fault," he added.

In Tuam, a town in western Ireland, a silent vigil was planned in solidarity with victims of "mother and baby" homes - institutions accused of being punishment hostels for unwed pregnant women.

Accusations of wide-ranging abuse in Irish Catholic institutions in Ireland date back several decades.

In a sign of the scale of the abuse, more than 14,500 people applied for compensation through an Irish government scheme for those abused at juvenile facilities run by religious groups.