A 23-year-old Australian woman was gored in the chest on the final day of Spain's San Fermin bull-running festival, where bulls chase people down the cobbled streets of Pamplona.
The woman was taken to hospital for surgery and was in a serious condition, health officials said.
Four more people injured in Sunday's run were taken to hospital but it was too soon to say how serious their injuries were, officials told reporters.
The Australian was struck by a massive Miura bull as she clung to wooden barriers yards outside the bull ring entrance. Other runners got tossed by the bulls or fell as they ran.
Miuras are renowned as Spain's largest and fastest fighting bulls, and Sunday's run was quick, taking two minutes, 16 seconds to cover 850m from stables just outside Pamplona's medieval stone wall to the central bullring.
On Saturday, a 19-year-old Spaniard was left in a "very serious" condition after runners fell and piled up at the entrance to the bullring, where the run ends.
At least two of the animals leapt over the pile, crushing runners under their hooves. Panicked festival-goers scrambled over those in front of them and others tried to pull the fallen free.
On Friday, three men were gored, including an American who had his spleen removed.
Running of the bulls dates back to the thirteenth century and was made famous internationally by Ernest Hemingway's novel The Sun Also Rises.
During the nine day fiesta every morning at 8am, six bulls specifically bred for fighting race through the narrow, medieval streets of Pamplona accompanied by an equal number of large steers - each wearing a clanking cowbell - tasked with keeping the pack tight and galloping at an even pace.
The animals will be killed by matadors in the final bullfight of the nine-day Fermin festival.
It attracts thousands of foreign visitors.