Madrid (CNN) -- The first day of the annual running of the bulls in Pamplona on Thursday was a swift race through old town for hundreds of runners trying to stay a step ahead of the raging bulls, but just four runners went to the hospital with injuries, officials said.
Commentators on Spanish state television TVE considered it a relatively safe start to the dangerous annual tradition in Pamplona, which has tallied thousands of injuries and 15 deaths since record-keeping began in 1924, including the fatal goring of a Spanish man in 2009.
The run in Pamplona started 400 years ago and became popular worldwide after author Ernest Hemingway wrote about it in the 1920s in his book "The Sun Also Rises," also published under the title "Fiesta."
It is now broadcast live across Spain by state television TVE, which pays Pamplona for exclusive rights, and positions some 20 cameras along the course.
A Red Cross official at the scene initially said just one runner went to the hospital, but the Navarra regional government issued a medical report later showing that four male runners were taken to hospitals.
The most seriously injured was a 40-year-old Spanish man who suffered broken ribs and a fractured shoulder blade and remained hospitalized later Thursday.
The other three were released from the hospital hours after arriving. They included two Spaniards, one with bruised ribs and the other with an eye injury, and a Panamanian man, 35, with a nose injury.
Television images showed numerous runners falling hard to the pavement and the bulls trying to step over them.
Most of the runners were men, mainly dressed in the traditional white outfits with red handkerchiefs, but there was also a small number of women.
The six bulls were from the Torrestrella breeding ranch and weigh between 470 kgs to 635 kgs (about 1,034 pounds to 1,397 pounds).
Accompanied by a pack of tame steers, they exited the corral just 10 seconds after the opening rocket was fired to signal the start of the run.
They moved quickly along the 825-meter (902 yard) course, and it took two minutes and 30 seconds until the bulls reached the corrals of the bull ring.
The bulls face certain death against matadors in a bullfight later in the day.
Pamplona's new mayor, Enrique Maya, told TVE just before the race that he had never run. He said he watched it from one of the numerous balconies along the course, which are filled with local residents or visitors, the latter typically paying top dollar for a safe vantage point.
The daily run continues for eight days, through July 14, at 8 a.m. (2 a.m. ET). It is the highlight of the San Fermin festival in Pamplona that attracts hundreds of thousands to the nonstop fiesta.