Ceuta, on Morocco’s northern coast, is separated from mainland Spain by the Strait of Gibraltar and has long been a focal point for migrants attempting to reach Europe.

Local officials had appealed to Madrid for help after a recent rise in attempted crossings, but there were chaotic scenes on Thursday as border controls apparently broke down.

Videos and images from Thursday show thousands of people swimming into the city, while local media reported crossings continuing into Friday.

The astonishing estimation by Spanish officials suggests the number of migrants who entered into Ceuta in the last day or so could be more than half of the population of the city – which sits at around 83,600 according to the latest local figures.

Spain has now deployed its armed forces to bolster security in Ceuta and at its sister city of Melilla, where between 300 to 400 crossings were also reported overnight.

Speaking on Friday during a visit to Ceuta, the prime minister condemned the crossings and said it was an attack on Spain’s territorial integrity.

Sánchez added that the government would be looking at reinforcing the border with Morocco.

The prime minister blamed the dangerous events on criminal networks manipulating the Supreme Court’s recent ruling, adding that incorrect information had “spread like wildfire in recent hours”.

He said authorities in Morocco were co-operating with plans to return those who had entered illegally.

Ceuta and Melilla trace their Spanish past to the 15th Century, and they have enjoyed a limited degree of self-government since 1995.

Coveted by Morocco, they have long been a flashpoint in diplomatic relations between the two countries.

They form the European Union’s only land borders with Africa.