The Spanish Red Cross said at least two people were gored in the penultimate running of the bulls at Pamplona's San Fermin festival.
Spokesman Alfonso Contin said one person was gored in the abdomen and another in the leg. There were no details regarding their identities.
The nine-day fiesta, held annually to honour the northern city's patron saint, dates back to the late 16th century. It became world-famous after Ernest Hemingway featured it in his 1926 novel "The Sun Also Rises" and attracts thousands of tourists every year.