Police in Spain and Gibraltar have smashed an unusual migrant-smuggling network which flew Moroccans into the tiny British territory then sneaked them over the border to Spain, arresting 47 people.

The trafficking ring, which had operatives in Morocco, Gibraltar and the neighbouring Spanish city of La Linea, managed to sneak more than 130 Moroccans into Spain, earning profits of more than a million euros (dollars), Gibraltar police said in a statement on Sunday.

Most of the migrants stayed in Spain but others travelled on to France, Italy and Belgium, with some currently facing immigration proceedings, a police source said.

In Morocco, the traffickers would compile a travel itinerary for each prospective migrant, including accommodation reservations and supported by "a dossier containing fraudulent supporting documents" to obtain a short-stay UK visa.

"Each migrant was charged between 7,000 to 8,000 euros in order to procure their visas," it said, explaining that such a visa was not good for entry into Spain or anywhere else in the passport-free Schengen zone.

More than 200 Spanish and Gibraltar police officers were involved in the operation that resulted in 44 arrests
More than 200 Spanish and Gibraltar police officers were involved in the operation that resulted in 44 arrests AFP / Handout

On arrival in Gibraltar, they would be picked up and sneaked over the border in a vehicle, usually at night, then housed in La Linea before being given coach tickets to destinations elsewhere in Spain or another European destination -- all of which cost them another 500-700 euros.

The probe began in November 2018 when police noticed "a significant increase" in Moroccan travellers from Casablanca and Tangiers arriving in Gibraltar, with investigators noting the "complexity, sophistication and efficiency" of the smuggling operation.

In a joint cross-border operation coordinated by Europol involving more than 200 officers, three people were arrested in Gibraltar and another 44 across Spain. Police also confiscated 19,000 euros ($21,000) in cash, five vehicles and 12 mobile devices.

Police believe the Moroccan branch earned profits of more than a million euros for obtaining the visas, while the traffickers in Spain and Gibraltar netted close to 80,000 euros.

"Gibraltar will not allow itself to be used by unscrupulous criminals who exploit the human suffering of migrants for economic benefit," said Ian McGrail, commissioner of the Royal Gibraltar Police.