A man gored in the neck is among five people hospitalised after the opening bull run at this year's San Fermin festival in Pamplona, according to officials in the northern Spanish city.

Key points: Five people were hospitalised after the first bull run this year, while 48 more were treated by the Red Cross

Five people were hospitalised after the first bull run this year, while 48 more were treated by the Red Cross The nine-day San Fermin festival sees bulls run through the streets in the morning before they are killed in afternoon bullfights

The nine-day San Fermin festival sees bulls run through the streets in the morning before they are killed in afternoon bullfights Animal rights activists have staged a naked lie-in to protest against the event

The man, a 46-year-old from the US, was speared by a bull's horn in the city's bull ring, at the end of the 850-metre course.

His injuries required surgery, the regional government reported.

A 23-year-old US man and a 40-year-old Spanish man were both gored in the thigh, while two young Spanish men sustained head injuries.

The Red Cross treated 48 other people with less serious injuries, including two who were trampled by the bulls.

Revellers from around the world flock to Pamplona every year to take part in the nine days of the running of the bulls. ( AP: Alvaro Barrientos )

The running of the bulls draws about 1 million spectators from around the world to Pamplona every year.

During the nine-day San Fermin fiesta, six bulls are run through the city's narrow streets every morning and then killed in afternoon bullfights.

This year's first run, which lasted two minutes and 41 seconds, came after the festival's official opening on Friday, when tens of thousands of party-goers showered each other with wine and champagne in a packed square.

The annual festival also includes music performances, traditional sports and dance displays, a religious procession on Sunday to honour the local patron, a firework competition and endless partying.

The running of the bulls in Pamplona draws about 1 million spectators every year. ( Reuters: Susana Vera )

Protesters say bulls at festival 'die in agony'

The festival regularly stokes debate about the treatment of animals.

On Friday, protesters lay half naked on the street with fake spears coming out of their backs to protest against what they said was the festival's cruelty.

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Animal rights group PETA posted on Twitter that the 54 activists represented "the bulls who will die in agony at the San Fermín Festival over the next week".

Runners are often injured at traditional bull runs in Spain, but no-one has died at Pamplona's San Fermin festival since Spaniard Daniel Jimeno was gored in the neck by a bull in 2009.