Rescuers are searching for two boats carrying dozens of migrants missing at sea between Western Sahara and the Canary Islands, as Spain continued to deport those who survived the perilous voyage from Africa's western coastline.

A spokeswoman for Salvamento Maritimo, Spain's coastguard, said on Wednesday a rescue plane was looking for two boats carrying 53 people, combing a huge area of water between the island of Gran Canaria and the port of Dakhla.

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On Tuesday, two nongovernmental organisations - AlarmPhone and Walking Borders - said 14 migrants, two of them children, had died off the coast of Morocco when their boat sank while en route to the Canary Islands.

The same day, Salvamento Maritimo rescued another boat in distress that was just south of Gran Canaria and carrying 25 migrants, taking them to the southern port of Arguineguin.

Meanwhile, Spain continued its efforts to send home those arriving without documents in the Canaries, a Spanish archipelago off the western coast of Africa, with a repatriation flight carrying 51 people leaving for Mauritania on Monday - the third such flight this year, the Spanish ombudsman said.

Such flights are operated by Frontex, the European Union's border security agency.

None of those on Monday's flight were from Mauritania, with 36 from Mali, 13 from Senegal, one from Gabon and one from the Ivory Coast. Another 88 people were flown back last month, among them 72 Malians.

Under a bilateral agreement between Spain and Mauritania, the latter agreed to receive any repatriated migrants who passed through its territory en route to the former, regardless of their nationality.

In the first six weeks of the year, the number of migrants reaching the Canaries soared to 1,008 - 15 times the level of a year ago, when it stood at 66, government figures showed at the weekend.

The surge has raised fears of a renewal of migrant traffic on a route taken by tens of thousands of people a decade ago.

Late last week, another 87 migrants, including one born while at sea, were rescued south of Gran Canaria. Nearly half of them were women and children.

As Morocco has waged a crackdown on undocumented immigration, there has been an increasing number of people trying to reach the Spanish islands by boat from Mauritania, whose coastline lies 1,000 kilometres (620 miles) to the south.

As well as taking the Canaries route, other migrants have sought to sail to mainland Spain from Algeria's northern coast.