During a TV address on Friday morning, Pedro Sánchez also vowed to "remain resolute in guaranteeing security in the face of any challenge, any eventuality and under any circumstances."
He was speaking from Ceuta, the Spanish autonomous city on the northern coast of North Africa which saw at least 60,000 migrants cross over from Morocco in recent days, according to Spanish authorities.
If the figure is confirmed, the event would be the largest single surge in irregular arrivals ever recorded on EU territory and Spain's biggest ever migrant crisis.
Most migrants came by sea, swimming from the Moroccan border town of Fnideq. They reached several beaches, especially El Tarajal, one of the closest to the border.
Sánchez also sent a message of support to the people of Ceuta, saying that "the whole of Spain stands with them" and acknowledging the "anguish" the population is going through. "We understand the emotional strain the people of Ceuta are under," he said.
