Pope Francis on Sunday urged world leaders to respond "decisively" after 700 migrants were feared drowned in the deadliest migrant shipwreck yet in the Mediterranean.

"These are men and women like us, brothers seeking a better life," the leader of the world's Roman Catholics said in his weekly address, urging leaders to "act decisively and quickly to stop these tragedies from recurring."

Urging the faithful in St Peter's square to pray for the victims, the pope added: "(They are) hungry, persecuted, injured, exploited, victims of war. They are seeking a better life, they are seeking happiness."

Francis has repeatedly highlighted the plight of migrants seeking to reach Europe clandestinely at the risk of their lives, famously railing against the "globalization of indifference" following shipwreck tragedies off the Italian island of Lampedusa in October 2013.

On Saturday he issued a fresh appeal to world leaders to act over this year's surge in the numbers attempting perilous sea crossings from North Africa.

"It is evident that the proportions of the phenomenon demand much greater involvement," he said then. "We must not tire in our attempts to solicit a more extensive response at the European and international level." AFP