Six foreigners were among seven people gored in a hair-raising second running of the bulls at Pamplona's San Fermin festival.
A 58-year-old Spaniard identified by the initials FLR, a 73-year-old South African man identified as MHO, and a Canadian aged 48, with the initials PCO, were in serious condition after being gored, a government statement said.
The regional government said one American, 55 and identified by the initials PGO, and another aged 23 with the initials WRO, were gored but their injuries were reported to be less serious.
A 46-year-old American with the initials JGO and an Indian aged 26, with the initials NSO, were also said to have suffered less serious goring injuries.
The regional government said nine others were taken to city hospitals for other injuries suffered in the run.
Several of the six bulls used got separated from the pack moments into the 8am run and began charging whatever came in sight.
The nine-day fiesta became world famous with Ernest Hemingway's 1926 novel The Sun Also Rises and attracts thousands of foreign tourists.
Runners dash along with six bulls down a narrow 930-yard course from a holding pen to Pamplona's bull ring. The bulls later face almost certain death in afternoon bullfights.
One runner, American Cindi Campbell, had a close call when she fell as one of the bulls ran behind her.
One man tried to protect her on the ground while husband Marshall Campbell pulled the beast away by the horn.
"This was my first and last time," said 53-year-old Ms Campbell, an accountant from Cave Creek, Arizona, who sprained her foot.
She said she had watched her husband and friend running on Thursday and thought the bulls would just pass her by.
The first one did but a second made a go for her.
"I'm lucky to be alive actually," she said. "I still say I'm glad I did it. Because if I hadn't done it I would regret it."
Another beast repeatedly tossed a man about before being lured away by other runners.
More than 1,000 people took part in the run, which lasted nearly six minutes, more than twice the normal running time. The bulls used weighed 1,170lb to 1,430lb.
Ten people were gored in the San Fermin festival last year. In all, 15 have died from being gored since record-keeping began in 1924.