Half-tonne bulls ploughed into a human pile-up in the Spanish city of Pamplona Saturday, leaving 23 injured, one seriously, at the celebrated San Fermin festival.
Bulls charged into the back of a pile of runners who were stuck in the narrow entrance to a bullring at the end of the short dash through the town's cobbled streets.
Two bulls leapt over the pile, crushing runners under their hooves. Panicked festival-goers in traditional white shirts and red neckerchiefs scrambled over those in front of them and others tried to pull the fallen free.
The rest of the animals -- of the six bulls and six steers that ran -- were herded to the arena through a side passage.
Several people were also trampled under the bulls' hooves during the crowded 850-metre (930-yard) run through the city's narrow streets, which lasted four minutes and 15 seconds.
It was the sixth day of the fiesta in this northern town, which draws festival-goers and daredevils from around the world for a week of drinking and perilous bull-runs.
Javier Sesma, head of the emergency unit of the local Navarra Hospital, told reporters that 23 people were hospitalised overall in the run and the pile-up.
These included a 19-year-old man from the Spanish town of Vitoria who was in serious condition with a chest injury, and an Irishman of 28 with a less severe injury, also to his chest.
The 19-year-old was "in an especially serious condition with a chest trauma causing breathing problems, and is requiring breathing apparatus," Sesma said. "He is in a stable but serious condition."
He added that two other people were being treated after being gored by the bulls' horns, with a Spaniard of 18 wounded in the armpit and a 35-year-old from Cleveland, Ohio, injured in the buttock.
Local government minister Javier Morras said the authorities were analysing exactly what caused the pile-up, which was broadcast live on public television.
Morras told reporters that one of the inner doors to the arena had got pushed shut in the rush, narrowing access and contributing to the pile-up.
Saturday's chaotic run nearly doubled the overall number of those hospitalised in the previous six days of bull runs, which had stood at 22 before Saturday's charge, according to the Navarre region authorities.
During Friday's run, bulls gored three men including a 20-year-old American.
Each year, hundreds of other people are treated by medics and the Red Cross at the scene for cuts and scrapes without being hospitalised.
Saturday's run involved bulls from the Fuente Ymbro ranch in Cadiz. It was more crowded than runs earlier in the week, with participation apparently swelled by weekend festival-goers.
The early morning bull runs are the highlight of the San Fermin festival, which was immortalized in Ernest Hemingway's classic 1926 novel "The Sun Also Rises" and now draws hundreds of thousands of tourists.
Fifteen people have been killed in the bull runs since records began in 1911. The most recent death was four years ago when a bull gored a 27-year-old Spaniard in the neck, heart and lungs.
The festival ends on Sunday.