The festival of San Fermin in the north of the country lasts for nine days and attracts thousands of people, who crowd the streets to run in front of the stampeding animals.

Monday morning saw the fourth run of this year's event so far, with at least seven people taken to hospital.

Among them was a 60-year-old Welsh man, according to reports.

The eight morning runs, known as encierros in Spanish, are the traditional highlights of the festival.

After the stampede, the bulls are then led to the bullring where they are typically made to run from one end of the arena to the other by a bullfighter, tiring them out.

The bulls are then usually killed by a matador. Only in rare cases, when the bull is deemed to have shown exceptional skill, is the animal pardoned.

Animal rights activists from PETA (People for the Ethical Treatment of Animals) and AnimaNaturalis campaigned against the tradition before the festival this year by donning red cloaks with horns.

Demonstrators have long protested against the bull runs.

Last year activists dressed up as dinosaurs and denounced the event as "prehistoric", and in the past, they have covered themselves in fake blood in protest.

PETA has gathered more than 70,000 signatures on its petition to urge the mayor of Pamplona to ban the bull run and replace it with a "humane alternative that does not involve animals".

The group's petition said: "At only 5 years old, bulls brought to Pamplona face a terrifying mob of people who chase them through the narrow streets of the city. They often lose their footing around corners and crash into walls, sometimes breaking bones or injuring themselves in other ways.

"They're then repeatedly taunted in the bullring, forced to run to the point of exhaustion, and stabbed with multiple weapons, enduring a slow, painful death. This cruelty is rightfully banned in many parts of the world.

"We, the undersigned, demand an end to this violence and urge you to replace the bull runs and bullfights with humane activities that don't involve animals."

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But the event began on Friday as usual.

Its origins date back centuries and reflect the historic practice of moving the bulls from fields outside the city, where they were bred, to the bullring.