According to the International Organization for Migration 42,500 migrants have arrived by sea in Spain since the start of the year and another 433 have been killed during the journey, often made aboard overcrowded and unseaworthy vessels.

The death toll is already three times higher than the figure for the whole of 2017.

The Spanish sea rescue service said on Twitter that 53 people had been rescued in the waters between Spain and northern Africa as migrant boat took on water.

However "two lifeless bodies" were also recovered.

The Caminando Fronteras NGO, which helps migrants, said that the dead bodies were those of two seven-year-old children.

Increasing numbers of Moroccans and sub-Saharan migrants are seeking to enter Spain, either by sea or by smuggling themselves into the Spanish enclaves of Ceuta and Melilla, which are in Morocco and are the only European territories in Africa.