Pope Francis was challenged by Belgian students Saturday about women's place in the Catholic Church, after paying tribute to a former sovereign who took a public stance against abortion.

The scripted yet frank exchange at a university in French-speaking Wallonia came after the 87-year-old pontiff was pressed on the issue of child sexual abuse, on day two of a visit partly clouded by past scandals.

In a letter on climate and development issues, read out loud to the pope, the Louvain-la-Neuve students questioned him on the Church's historical part in entrenching female subservience, the unfair division of labour and even disproportionate female poverty.

"Throughout the history of the Church, women have been made invisible," the letter read. "What place, then, for women in the Church?"

Francis replied by saying the Church was female, noting that the Italian word for it, 'chiesa', is a feminine noun.

"A woman within the People of God is a daughter, a sister, a mother," he said, adding "womanhood speaks to us of fruitful welcome, nurturing and life-giving dedication".

He did not give any details about potential plans for reform.

His response did little to satisfy critics. In a statement issued shortly after the exchange, the university expressed its "incomprehension and disapproval" at his stance.

"We are really shocked," said Valentine Hendrix, a 22-year-old student. "He reduces us to a role of childbearer, mother, wife, everything we want to emancipate ourselves from."

Jean-Pascal van Ypersele, a climatologist at UCLouvain university, said Francis had "failed to rise to the occasion."

"To reply that the Church is a woman is really missing the point of the question -- about the Church's respect for women and their role in the institution and in society," he said.

Earlier the pope visited the tomb of Belgium's King Baudouin who in 1990 famously refused to sign a law lifting penalties against abortion, citing personal convictions.

Francis described the legislation -- passed after the king temporarily renounced his functions to avoid having to endorse it as "a murderous law".

The Catholic Church has been led for 2,000 years by men, opposes abortion and female priesthood and does not recognise divorce.

The Argentinian pope has welcomed discussions on a greater role for women in the Church, but allowing female deacons who are able to celebrate baptisms, marriages and funerals but not masses -- is highly contentious.

The latest controversy comes a few days before the opening of the Synod of Bishops, an initiative launched by Francis to bring the Church closer to the faithful, in which bishops, clergy and laypeople share views on topics as diverse as gender issues and priestly celibacy.

The pope's three-day Belgium visit has been dominated by the Church's dark legacy of child sexual abuse, and saw him meet on Friday with 17 victims.

The group shared their stories and expressed their expectations to the pope, who "took note" of their requests, according to the Vatican.

Belgium has been rocked by decades of abuse scandals and cover-ups and a hard-hitting documentary last year put the issue back on front pages, prompting new victims to come forward.

In an open letter this month, some had demanded the pontiff address paedophilia and set up a process for financial reparations.

On Saturday morning, during a gathering with clergy and pastoral workers at the vast Basilica of the Sacred Heart in Brussels, Francis was pressed on the issue for a second day running.

Replying to a question by a representative of an organisation helping abuse victims, the pontiff acknowledged the "atrocious suffering and wounds" caused by the Church.

"There is a need for a great deal of mercy to keep us from hardening our hearts before the suffering of victims, so that we can help them feel our closeness," Francis said.

"We must learn from them, as you said, to be a Church at the service of all without belittling anyone."

A day earlier, Francis had said the Church must "seek forgiveness", calling child sexual abuse "our shame and our humiliation," after being questioned on the issue by King Philippe and Prime Minister Alexander De Croo.

The visit by Francis will culminate on Sunday with an open-air mass in a Brussels stadium. (Courtesy, excluding headline, AFP)

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