A boat carrying migrants capsized off Spain's Canary islands overnight, killing at least nine people and leaving 48 missing, the national maritime rescue service said on Saturday.

Eighty-four people were on board and 27 were rescued after rescuers responded to a distress call received shortly after midnight from off El Hierro, one of the islands in the archipelago, a statement said.

This follows the death of 39 migrants in early September when their boat sank off Senegal while attempting a similar crossing to the Canaries, from where migrants hope to reach mainland Europe.

Thousands of migrants have died in recent years setting off into the Atlantic to reach Europe onboard overcrowded and often dilapidated boats.

In late August, Spain's prime minister visited Mauritania and The Gambia to sign cooperation agreements to crack down on people smugglers while expanding pathways for legal immigration.

As of August 15, 22,304 migrants had reached the Canaries since the start of the year, up from 9,864 in the same period the previous year.

The Atlantic route is particularly deadly, with many of the crowded poorly equipped boats unable to cope with the strong ocean currents. Some boats depart African beaches as far as 1,000 kilometres (620 miles) from the Canaries.

The International Organization for Migration, a UN agency, estimates that 4,857 people have died on this route since 2014.

Many aid organisations say that's a massive undercount, with Caminando Fronteras, a Spanish NGO that aids migrants, saying 18,680 have died trying to reach Europe.

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© Agence France-Presse