Navarra Hospital chief Javier Sesma said the person sustained neck injuries in a fall in the fifth run of the famed San Fermin festival.
However, he said no one was gored along the 930-yard (850-metre) route to Pamplona's bull ring.
There were moments of tension when a bull became separated from the pack and looked as if he would charge some of the runners. He was eventually guided into the ring without incident.
The nationally televised morning runs are the highlight of the nine-day street festival that became world-famous after Ernest Hemingway's 1926 novel The Sun Also Rises.
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