Half-tonne fighting bulls thundered into and knocked over daredevils on a break-neck bull run through the cobbled streets of Spain's northern city of Pamplona on Wednesday that sent three men to hospital.
No one was gored but three Spaniards, aged 24, 27 and 32, suffered bruises in falls and were taken to hospital, regional health officials said.
Dozens of other runners were treated at the scene for scrapes and other more minor injuries.
The six bulls from the Victoriano del Rio ranch took just two minutes and 14 seconds to complete the 848-metre course from a holding pen to the city bull ring.
It was the fastest time of the four daily bull runs held so far this year at the nine-day San Fermin festival.
Hundreds of runners, most wearing traditional white clothing and red kerchiefs around their necks, tripped over each other or fell in the mad rush but avoided getting caught by the bulls' horns.
"It was thrilling, unforgettable, amazing. I don't think I have ever felt so exhilarated in my life. I am really glad I came and experienced this," said 26-year-old law student Dale Carpenter from Ohio in the USA, who included Pamplona on his tour of Europe so he could take part in the festival.
Runners crammed together against the walls of buildings along the route as the herd raced by.
One man who fell as the animals approached lay on his side with his hands holding his head as the beasts charged by him. He then got up and ran to the side of the route.
A firework set off the race at 8 am, releasing the six bulls and six steers, castrated bulls that keep the herd together, through the narrow streets.
People clung to street lights and climbed on the double wooden fence lining the route to get a better view or watched from apartment balconies.
A large black bull tripped and fell just before the herd reached the bull ring and became separated from the pack as runners scrambled to get out of its way.
Late in the afternoon the bulls will face matadors and be killed in the ring, with their meat served up in some of Pamplona's best restaurants.
People from around the world flock to the city of 200,000 residents to test their bravery and enjoy the festival's mix of round-the-clock parties, religious processions and concerts.
The nine-day fiesta, which was immortalised in Nobel prize-winning author Ernest Hemingway's 1926 novel "The Sun Also Rises", lasts until July 14.