Up to 57 people have died after a ship from Gambia carrying around 150 migrants sank off the coast of Mauritania on Wednesday, the UN migration agency said.

The perilous sea passage from West Africa to Europe was once a major route for migrants seeking jobs and prosperity. This incident is one of the deadliest since attempts became scarcer when Spain stepped up patrols in the mid-2000s.

"Mauritanian authorities say up to 57 people are dead after a vessel carrying migrants sank off its coast today," the International Organization for Migration (IOM) said on Twitter.

"Survivors told IOM staff the vessel left the Gambia last Wednesday with at least 150 people aboard."

Although home to some of the continent's fastest-growing economies, West Africa is struggling to generate enough jobs for its mushrooming young population. As a result, migrants continue to tackle treacherous routes to get to Europe.