Straggling bull skewers runners in Pamplona

A straggling half-tonne fighting bull skewered two Britons and an American on Monday as it turned its horns on panicked runners in Spain's Pamplona bull run.

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  black bull, called Fugado (Escapee), hung back and confronted the crowd.

Three gored in Pamplona bull run

RAW VISION: Two Britons and one American are gored in Monday's running of the bulls through the streets of Pamplona in northern Spain, the regional government says.

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 wooden barriers on 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 three minutes and 37 seconds to cover the 850-metre course.

"As I was running at one point I thought I would dive under the barriers because I thought this isn't looking so good," said Jeannie Mark, a 41-year-old Canadian and one of the few women taking part.

"There were a lot of people around me and pushing me and I thought I might get in a bad situation here. Then I decided to keep going," said Mark, who works as a teacher in China.

"You have to make quick decisions during the run."

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

Many people confess to being lured to the alochol-soaked festival by Ernest Hemingway's 1926 novel featuring the bull running, The Sun Also Rises.

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 during the July 6-14 festival, which dates back to medieval times.

But the Navarra Hospitality Association predicts that hotel occupancy in Pamplona during the fiesta, a mix of drinking, religious ceremonies and morning bull runs, will be down by around 10 per cent over last year.

With Spanish regions under pressure to rein in deficits, the budget for the San Fermin festival this year was slashed by eight per cent over 2011 to 2.4 million euros ($A2.9 million), its fourth straight annual decline.

Pamplona officials are banking on the festival bringing in more than 70 million euros in tourism earnings this year.

Bars are allowed to remain open until 6am during the fiesta, and the event accounts for up to a third of total annual sales at some establishments in the centre of the city.

The bull runs are thought to have started when butchers began running ahead of the beasts they were bringing from the countryside to the San Fermin festival.