A fighting bull skewered a 'reckless' Australian thrill-seeker in the leg on Friday after he taunted the beast in Spain's San Fermin fiesta, organisers said.

The half-tonne bull pierced the tourist's right thigh with its horn and tossed him across the sand of the bull ring in the final stage of a daily bull-run in Pamplona, northern Spain.

Doctor's in the bull-ring's surgery treated the man for damage to a major artery and his condition had improved, said a spokeswoman for the festival organisers.

The pack of six massive bulls and six steers thundered 846.6 metres through the winding streets of Pamplona from a holding pen to a bull-fighting ring in three minutes and 10 seconds, organisers said.

Thousands of runners, most dressed in white with red handkerchiefs, surrounded the charging bulls, some a few paces in front of the beasts' horns and others slapping them from the side or behind.

But once the herd entered the ring, the Australian tourist, dressed in a T-shirt and short jeans with a red bandana around his waist, started waving his arms in the air, running and jumping behind a bull.

When the powerful beast turned towards him, the man tried to switch direction but slipped and tumbled in the sand.

The bull lowered its head and drilled a sharp left horn into the man's right thigh, tossing him across the ground and then pushing its head into the man's back.

Other runners scrambled to distract the bull from its attack: one waved a matador's cape at the bull's head and another pulled its tail until the beast moved away.

The Australian, whose name was not given, stood up after his mauling, shown to millions on live television.

"He was reckless, that was really bad, you should not do that," said the festival spokeswoman.

"He is being treated in the bull ring surgery, one of his main arteries in the thigh was affected but his status is now less serious."

At least three other runners, whose nationalities were not given, suffered minor injuries including bruising to the face and back during the run, organisers said.

Four runners were also injured in the inaugural bull run on Thursday, a centrepiece of the alcohol-charged festivities popularised worldwide by Ernest Hemingway's 1926 novel The Sun Also Rises.

The city of some 200,000 residents expects the festival, which runs to July 14, will lure at least as many tourists as last year when 1.5 million people turned out and hotels reported a 95-per cent occupancy rate.

Every year between 200 and 300 participants in the run are injured. Most are hurt after falling but some are trampled or gored by the bulls despite increased safety measures.

The most recent death occurred two years ago when 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.

This year organisers have launched a free iPhone app in English to help revellers to assess their chances of emerging from the bull runs intact.

It asks users about their behaviour at the festival, including how much they have had to drink and how many hours of sleep they have had.

In the evenings after the daily chase, the beasts are killed in the bull ring and their meat is served up in city restaurants.