MADRID - An unusually large group of about 5,000 Moroccans, many of them minors or families, illegally swam into Spain's northern African enclave of Ceuta on Monday, a spokesman for the Spanish government's delegation there said.
One person died in the attempt, the spokesman said.
Crowds of mostly young people swam onto the beach, some running or showing thumbs up, footage by local media Faro showed, in activity that started overnight and gathered pace later in the day.
The Spanish enclaves of Ceuta and nearby Melilla on Morocco's northern coast have long been a magnet for African migrants trying to reach Europe in search of a better life.
But Monday's high number - which included about 1,500 minors, the spokesman said - was swiftly followed by an announcement by Spanish authorities that they would increase their security presence in the area.
Spain will "keep a cool head," Foreign Minister Arancha Gonzalez Laya told Cadena SER radio, adding that authorities had already started sending those who had just arrived back to Morocco.
Spanish and Moroccan authorities had contacts in the afternoon over what was happening in Ceuta, she said.
The arrival of the migrants took place at a time of increased tension between Spain and Morocco over the fate of Brahim Ghali, leader of the Algeria-backed Polisario Front, who is in hospital in Spain.
Morocco's Foreign Ministry issued a strongly worded statement last month deploring what it said was the decision of Spain to admit Ghali under a false identity without informing Morocco, and saying Spain's decision would have repercussions for their relations.
The United States in December recognised Moroccan sovereignty over the Western Sahara territory, which is also claimed as an independent state by the Polisario Front.
Ghali is hospitalised in Spain, a Spanish diplomatic source told Reuters.
Ghali was accepted into Spain on humanitarian grounds, Gonzalez Laya told Cadena SER radio, adding that she believed the migrant influx was not in retaliation over the Polisario Front leader's fate.
"I cannot speak for Morocco but what they have told us a few hours ago, this afternoon, is that this is not due to the disagreement (over Ghali)," Gonzalez Laya said.
"Spain has been very clear and detailed about the case. It's simply a humanitarian issue," she said.