A bull gored three men after breaking away from the pack chasing crowds through the streets of Pamplona in the closing run of Spain's San Fermin festival on Monday.
The animal charged several runners in the town, lifting at least two of them off the ground on its horns and ripping through their legs.
Two Australian men were wounded - one of them, a 26-year-old, seriously - alongside a Spaniard, 21, from the surrounding Navarra region, said authorities.
For a week every July, hundreds of people dressed in white with red scarves join the daily "encierros", when bulls chase them through the town's narrow streets into the bull ring in a festival that has grown into a global tourist attraction.
Several men have already been gored this year but Monday's run, the eighth and last, was particularly brutal.
Other participants tried to distract the bull - one of a pack of six - and eventually herded it into the ring. The runs usually last between three to five minutes, and the bulls then appear in an evening bullfight, when they are killed.
Four other people, including one woman, were taken to hospital on Monday with injuries, medical authorities said.
Nine men, one of them a 23-year-old Briton, were still in hospital on Monday recovering from injuries from the past week, according to the Navarra region's hospital authorities.
Another of the injured was Bill Hillmann, an American who co-wrote a book called "Fiesta: How To Survive The Bulls of Pamplona". He was gored in the thigh after he tripped and fell.
Many participants drink and dance all night before taking part in the 8 a.m. (0600 GMT) event, though local authorities have tried to clamp down on reckless behaviour in recent years.
Spanish media said over the weekend that Pamplona police were looking for a young man who was photographed trying to get a dangerous "selfie" photo of himself on his phone as he ran inches in front of the bulls.
He could be fined up to 3,000 euros ($4,100) if they find he endangered other runners.
A 27-year-old man from Madrid was the last person to be killed during a Pamplona bull run after being gored in the neck in 2009. There have been 14 fatalities over the past century at the fiesta, which dates back to the 13th century and was depicted in Ernest Hemingway's novel "The Sun Also Rises".
Few women take part in the run.