Pope Francis launched a global Roman Catholic campaign on Wednesday to improve the lot of immigrants and one of his top cardinals urged politicians to "touch the hand of a migrant" before trying to stereotype them.

The two-year "Share the Journey" campaign comes at a time of growing anti-immigrant sentiment in the United States and many European countries where far-right parties have made inroads.

On Sunday the far-right, anti-immigrant Alternative for Germany (Afd) party surged to third place in a national election, tapping into public disquiet over the arrival of more than a million migrants in Germany over the past two years.

The pope, who has made defence of migrants a major plank of his pontificate, launched the campaign in comments to tens of thousands of people in St. Peter's Square for his weekly audience, urging Catholics around the world to be "open, inclusive and welcoming".

Italy's anti-immigrant Northern League has vowed to clamp down on migration from developing countries if it takes power in a coalition government after next year's elections.

At a news conference at the Vatican, Cardinal Luis Antonio Tagle of Manila called for a "culture of personal encounter" where friendship supplants fear.

"I would invite the leaders to meet a migrant, touch the hand of a migrant, smell a migrant, listen to their stories and you will see that they are like you and me," he said.

"They are not really 'other'. They could be me. They could be my brother, my sister, my parents," said Tagle, whose grandfather left China for the Philippines as a poor boy.

"LOOK THEM IN THE EYES"

The two-year campaign of "action and awareness" is being spearheaded by Caritas Internationalis, the worldwide umbrella of Catholic charities.

The campaign encourages local communities to facilitate encounters between migrants and those who fear or denigrate them in church halls and private homes.

"Look them in the eyes, listen to why they left their homes, how their journey's been, see the real people behind the numbers and scare stories," Tagle said.

He urged politicians "not to close the doors on people who might enrich your society".

In the United States, where President Donald Trump wants to build a wall along the border with Mexico, his ex-chief strategist Steve Bannon - himself a Catholic - got embroiled in a row with the U.S. Catholic Church this month when he said its bishops backed illegal immigrants in order to fill empty pews.

Francis this month said he hoped Trump would re-think his decision to end a programme protecting undocumented immigrant children, saying it was important for young people to have roots.