In what he called an "appeal to the conscience" of politicians in Europe and the international community, the first US pope said "human dignity has no passport and does not lose its value when crossing a border".
"We cannot grow accustomed to counting the dead," said the Pope on Thursday at Gran Canaria's Port of Arguineguin, dubbed the "Dock of Shame" by relief organisations after some 1000 migrants were stranded in squalid conditions there in the early months of the coronavirus pandemic.
"May history not accuse us of turning the pain of those who suffer into a common sight along our shores," he urged thousands gathered near a memorial to migrants lost at sea.
"Sooner or later, it will be known whether we protected life or whether we yielded to indifference."
Leo, who has adopted a more forceful tone against the direction of global leadership in recent months, recently drew the ire of US President Donald Trump after sharply criticising his hard-line, anti-immigrant policies.
The Pope is visiting the archipelago off the western coast of Africa, one of Europe's migration hotspots, as the centrepiece of a week-long tour of Spain on which he will meet with some 1000 migrants on Friday.
The islands are a destination for migrants taking a deadly journey through Atlantic waters, often in improvised and overcrowded small crafts.
In Thursday's meeting at the port with recently arrived migrants and representatives of the church and humanitarian organisations that care for them, the Pope heard from volunteers and others, including a rescue boat captain who said that in 18 years he and colleagues had saved some 20,000 migrants.
"It's a number that makes me sick and that you cannot forget," said the captain, Tito Villarmea.
"I wish we didn't have to save anyone."
More than 1000km from mainland Spain, the Canaries received a record 46,843 irregular migrants in 2024, compared with fewer than 1000 in 2015, according to official data.
More than 3000 people died in 2025 trying to reach the islands, according to the NGO Caminando Fronteras.
Leo told the Spanish parliament on Monday that a lack of help for the world's migrants was challenging "the ethical foundation of the international order".
On Thursday, he called for "legal and safe pathways" for immigration, international co-operation to fight human trafficking, and funding to rescue migrants in distress at sea.
The world must do more to eradicate poverty, wars and corruption that forces migrants to flee their homes, he said.
