Pope Leo has told Christians that the Christmas story should remind them of their duty to help the poor and strangers.

In his Christmas Eve sermon, the pope said the story of Jesus being born in a stable because there was no room at an inn showed followers that refusing to help those in need was tantamount to rejecting God himself.

Leo, who has made care for immigrants and the poor key themes of his early papacy, said Jesus’ birth showed God’s presence in every person as he led the world’s 1.4 billion Catholics into Christmas at a mass in St Peter’s Basilica.

“On earth, there is no room for God if there is no room for the human person. To refuse one is to refuse the other,” said the pope during the solemn service, attended by about 6,000 people inside the basilica.

Leo, the first US-born pope, is celebrating his first Christmas after being elected in May by the world’s cardinals to succeed the late Pope Francis. The pope, who has criticised Donald Trump’s divisive immigration crackdown, quoted a line from Pope Benedict XVI lamenting that the world does not care for children, the poor or foreigners.

“While a distorted economy leads us to treat human beings as mere merchandise, God becomes like us, revealing the infinite dignity of every person,” said Leo. “Where there is room for the human person, there is room for God. Even a stable can become more sacred than a temple.”

Outside the basilica, about 5,000 people watched the service on screens from St Peter’s Square, holding umbrellas and wearing ponchos under a hard rain in Rome.

Leo, 70, came outside to greet them before the start of the mass. “I admire and respect and thank you for your courage and your wanting to be here this evening, even in this weather.”

On Thursday, the pope will celebrate a Christmas Day mass and deliver a twice-yearly Urbi et Orbi (to the city and the world) message and blessing.

- Agencies