A U.S. tourist was gored by a bull on Friday along with two Spaniards as they all took part in a bull-run in Pamplona, where people race through the Spanish town's cobbled streets pursued by the animals.
Authorities did not give details on the 20-year-old American's condition. One of the Spaniards was described as having "less serious" injuries.
A further three bull-runners were injured, including another American, aged 48. Authorities did not specify their injuries, but participants are often hurt due to falling in the chaotic dash. All the injured were men; few women take part in the run.
The gorings were the first this year at the festival, which started on Sunday and includes a daily bull run starting at 8 a.m. (0600 GMT) that usually lasts between two and five minutes.
Pamplona's San Fermin festival, one of hundreds of bull-running fiestas held around Spain every year, was made famous by Ernest Hemingway's novel "The Sun Also Rises" and attracts visitors from around the world.
Many participants, dressed in white with red kerchiefs round their necks, drink all night before the early morning run.
A 27-year-old 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 that dates from the 13th century.