The service said its crews had rescued 293 people from nine boats on Saturday. On Sunday, a further 250 migrants were rescued from eight boats, three of which were in poor condition and later sank, they added.
The migrants were from various countries in North and sub-Saharan Africa.
On a single day in August last year, Spanish rescuers saved 593 people from 15 small paddle boats – including 35 children and a baby – after they attempted to cross the seven-mile Strait of Gibraltar.
According to statistics from the International Organisation for Migration (IOM) 21,468 migrants and refugees arrived in Spain by sea in 2017, with 224 people dying on the journey.
The arrival figures showed a threefold increase on 2016, when 6,046 people reached Spain and 128 people died en route.
By early May this year, 4,409 people had reached Spain and 217 people had died in the attempt.
The UN refugee agency, UNHCR, has already warned that Spain is facing “another very challenging year” when it comes to helping and protecting those arriving on its shores.
“This situation requires urgent measures from the central government, which needs to coordinate with the relevant ministries as well as the Guardia Civil border police, the maritime rescue service, the police and NGOs,” said María Jesús Vega, a spokeswoman for UNHCR Spain.
Vega pointed out that almost as many people had died trying to cross the Mediterranean to Spain in the first five months of 2018 as had died in the whole of 2017.
“Government action is more urgently needed than ever and we need to see proper infrastructure for welcoming, registering and identifying these people,” she added.
“All the organisations working on this situation are overwhelmed.”
The Spanish government says it has spent more than a decade trying to develop a policy that reduces migration by helping potential migrants to remain in their own countries.
“The solution to irregular immigration is necessarily a matter of creating opportunities in countries of origin and working to improve the paths of legal migration,” a spokesman for the interior ministry had said in January.
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