The bull lagged behind in the pack of six huge bulls and six steers that tore through the northern city's slippery cobbled streets, surrounded by crowds of thrill-seekers dressed in white with red neck scarves.

As the beasts thundered from a holding pen to the Pamplona arena, the 550-kilogramme (1,200-pound) black bull, called Fugado (Escapee), hung back and confronted the crowd.

Some people tried to keep it at bay with long sticks, but the bull stopped and then charged into a crowd of runners cowering by the side of the road, its horns lowered.

"My God," a man watching the scene could be heard crying out.

The bull repeatedly stopped and turned back to challenge people behind it, before finally being coaxed to finish the run, a centrepiece of the annual San Fermin festival.

Fugado skewered three runners with its horns, none seriously: a 20-year-old Briton in the right leg; a 29-year-old Briton in the left leg and a 39-year-old American in the right knee, regional health authorities said.

Another four people were injured: a 38-year-old American bruised his knee and ankle; a 30-year-old Spaniard dislocated his shoulder; and two 32-year-old Spaniards hurt their ankles.

The bulls took just three minutes and 37 seconds to cover the 850-metre (2,800-foot) course.

Last year 20,500 people took part in the festival's eight bull runs, nearly half of them coming from abroad, mostly the United States, Australia and Britain.

Three years ago a bull gored a 27-year-old Spaniard to death, piercing his neck, heart and lungs with its horns in front of hordes of tourists.

Pamplona officials expect about half a million people will flock to the city of 200,000 residents during the festival, which dates back to medieval times.