At least 69 people have died and many more are missing after a boat capsized off the coast of Mauritania, coastguards in the north-west African country have said.

Seventeen people have been rescued and a search is continuing for other passengers who were aboard the dugout canoe that was heading towards Spain's Canary Islands.

According to survivors, the boat left The Gambia six days before Tuesday's accident, carrying around 160 people on board, mainly Gambian and Senegalese nationals.

The perilous journey over the Atlantic Ocean has become an increasingly common route for African migrants trying to reach Europe.

Nearly 47,000 people reached the Canary Islands last year, and the Spanish non-government organisation Caminando Fronteras estimates more than 9,000 migrants died trying.

Coastguard sources told Spanish news agency EFE that search efforts were ongoing off the coast around 60km (37 miles) north of the capital, Nouakchott - and rescue teams were preparing to dive and inspect the sunken vessel.

The migrants spotted the lights of a coastal town late on Tuesday night and "moved to one side, causing it to capsize", a senior coastguard official told the AFP news agency.

Caminando Fronteras spokesperson Helen Maleno urged the coastguard to keep up the search, describing the accident to Spanish media as one of the most significant "tragedies of this summer".

Earlier this week, the Mauritanian security forces were accused of systematically abusing migrants from other African countries.

The Human Rights Watch report alleged the violations had been exacerbated by a deal with the European Union and Spain, which aims to curb the dangerous sea crossings to the Canary Islands.