About 6,000 African migrants have died or gone missing on the sea journey to the Canary Islands in 2006, Spanish immigration officials say.
Africans are attempting risky sea journeys to reach Europe
They say more than 31,000 migrants reached the islands in the Atlantic - more than six times as many as in 2005.
The coastguard intercepted fewer than 5,000 of them in small wooden - and often overcrowded - boats.
The Canaries is one of the most popular destinations for Africans trying to reach Europe to escape poverty.
"We're talking about a dramatic number of dead," Froilan Rodriguez, the Canary Islands' deputy director of immigration, told Spain's Cadena Ser radio station.
Mr Rodriguez said that about 600 bodies had been picked up on the shores of the Canaries and the African mainland in the past 12 months, but the total of migrants killed had been about 10 times higher.
Jose Segura, Spain's interior ministry official in the Canaries, said that almost as many Africans had reached the islands in 2006 as in the previous four years combined.
He described the increase in the numbers of the arrivals as "spectacular".
Spain has repeatedly called for more European Union help to deal with the problem, the BBC's Danny Wood in Madrid says.
In a bid to stop this migration, boats, planes and helicopters from the European Union's border control agency are now patrolling the shores of Senegal and Mauritania, our correspondent says.