About 60,000 migrants crossed from Morocco into Spain’s tiny Ceuta territory in the past 24 hours, Ceuta’s president said Friday, a figure that is equivalent to 70% of the population of the city in North Africa. At least 57 migrants died on the journey.

But roughly half of the people who made the crossing soon made their way back voluntarily, the Spanish government said, after the sudden arrival of so many migrants triggered chaos and a humanitarian crisis.

Some migrants swam several miles through the sea and faced down authorities who tried to turn them back with water cannons, tear gas and warning shots. Those who died included some who drowned or were killed in a stampede to cross a breakwater barrier near a border checkpoint.

Spain deployed its armed forces and additional police to restore order in Ceuta, which sits on the Strait of Gibraltar at the entrance to the Mediterranean Sea and has been a Spanish possession since 1580. On the Moroccan side of the border, security forces clashed with migrants.

“The situation that Ceuta is going through is absolutely unsustainable,” Ceuta President Juan Jesús Vivas told journalists.

Meanwhile, migrants from Morocco also attempted to cross into Melilla, Spain’s other territory at the tip of North Africa, where they clashed with police.

Border surge linked to Supreme Court ruling

The authorities in Ceuta and Madrid have linked the border surge to a recent decision by the Spanish Supreme Court, which ruled that migrants arriving by sea could not be summarily deported, unlike those who cross by land or climb the border fence.

Sánchez said migrant smugglers misinterpreted the ruling.

The interpretation of the Supreme Court’s ruling “spread like wildfire over the past few hours through the networks of human trafficking organizations,” triggering the surge, Sánchez said.

Spanish prime minister has bucked anti-immigration trend

Sánchez has bucked the anti-migration trend that has gained ground across Europe and in the U.S.

Earlier this year, his government moved to give residency and work permits to hundreds of thousands of migrants already living in the country without permission.

Sánchez, a Socialist, argued that it would be good for the economy and the demographics of an aging Spain. Migrants who entered irregularly after Jan. 1 this year were not included.

His critics have jumped at the opportunity to attack his policy, saying it encouraged more migrants to come.

Sánchez on Friday defended his migration policy and distanced it from the events in Ceuta.

Middle East Monitor: Ceuta crisis sparks online speculation over Israel’s role in pressuring Spain

The speculation intensified after social media users resurfaced articles published earlier this year by pro-Israel analysts who argued that Israel and the US should aid Morocco over its claim to Ceuta and Melilla as a means of pressuring Spain.