The new Pope, Leo XIV, has called for the Catholic Church to "desperately" counter a lack of faith in his first mass at the Vatican.

Speaking the day after he was elected as the 267th Pope and first US leader of the Church, he warned that people were turning away from faith and instead to "technology, money, success, power, or pleasure".

Leo said he had been elected to be a "faithful administrator" of a Church that would act as a "beacon that illuminates the dark nights of this world".

The ascension of Robert Francis Prevost has been celebrated by the world's 1.4 billion Catholics, with joyous outbursts in his US homeland and in Peru, where he served for 20 years.

In his sermon on Friday, the new Pope said there were many settings where the Christian faith was considered "absurd" - with power, wealth, and technology dominating - but it was precisely there that missionary outreach was needed.

"A lack of faith is often tragically accompanied by the loss of meaning in life, the neglect of mercy, appalling violations of human dignity, the crisis of the family and so many other wounds that afflict our society," he said in the address delivered in Italian.

Pope Leo, 69, wore a white papal robe trimmed in gold as he addressed the seated cardinals in the Sistine Chapel, an event broadcast live by the Vatican administration.

In an unscripted introduction before the homily, Leo also called on Church unity from his cardinals, telling them in American-accented English: "I know I can rely on each and every one of you to walk with me".

Following weeks of anticipation, the previously-unknown Prevost was introduced as the new Pope to the world on Thursday evening in St Peter's Square.

Tens of thousands of worshippers in the square burst into cheers when white smoke curled out of the Vatican's chimney on the second day of the conclave's voting.

Shortly after, the Chicago-born Prevost appeared on the balcony of St Peter's Basilica. In his first words to the crowds he outlined a vision of a "missionary" Church which "builds bridges, which holds dialogues, which is always open".

He echoed his predecessor, the late Pope Francis, in calling for peace.

"Help us, and each other, to build bridges through dialogue, through encounter, to come together as one people, always in peace," he said.

World leaders have rushed to congratulate Prevost on his election, pledging to work with him on global issues amid uncertain times. US President Donald Trump called it a "great honour" to have the first American pope.

Prevost, who had previously been the Bishop of Chiclayo in Peru, was only made an archbishop and then cardinal in 2023. He was elected by his fellow cardinals in what is believed to be four rounds of voting in the secret conclave that took place two weeks after Francis died.

He is seen as being aligned with the progressive late Pope, who was viewed as a champion of human rights and the poor and celebrated for his charismatic style that sought to make the Catholic Church more outward-facing.

Vatican watchers have noted that Francis appeared to have brought Prevost to Rome in recent years, perhaps to set him up as a potential successor.

The Augustinian missionary worked for decades with the poor and marginalised in Peru, where he obtained nationality in 2015.

In his previous role as Cardinal Prevost, he had also expressed or amplified criticism of the US administration under President Trump, including its anti-immigration policies.

On his X account in February, he had criticised Vice President JD Vance's argument that Christians should love their family, neighbours, community and fellow citizens in that order, saying: "JD Vance is wrong: Jesus doesn't ask us to rank our love for others".

As Pope he faces a momentous task in leading the Church in a time of significant global conflicts. Observers have expressed hope that he can offer a counterpoint to more divisive voices on the world stage.

His upcoming remarks, which include Sunday's midday Regina Coeli prayer in St Peter's Basilica and a Monday news conference with journalists, will be closely watched for signs as to which direction he intends to lead the Church and what kind of Pope he will be.