Pope Francis on Saturday told refugees trapped on the Greek island of Lesbos that they are "not alone" in their plight, and called on the world to respond with "common humanity" to the migrant crisis.

"You are not alone... do not lose hope," the pope said as he visited Lesbos with Ecumenical Patriarch Bartholomew and Archbishop Ieronymos, the head of the Church of Greece, calling on the world to respond to the tragedy "in a way worthy of our common humanity".