The running of the bulls at the San Fermin festival in Pamplona, northern Spain Reuters

Two young Britons and an American have been gored during the famous San Fermin bull-run in the northern Spanish city of Pamplona as foreigners once more became the favoured target of the festival's fighting bulls.

The two unnamed Britons, aged 20 and 29, were both gored in the leg after one bull turned back on the runners and attacked a mass of people cowering against the barriers marking the course.

Television pictures showed the 550kg bull, called Fugado, lowering his horns and ploughing into a group of runners wearing the traditional white and red San Fermin colours towards the end of the 850-metre run.

A 38-year-old American from Philadelphia was also gored, making this the most dangerous San Fermin bull-run since a 27-year-old Spaniard was killed in 2009. On that occasion the bull also turned on its tracks and gored Daniel Jimeno through the neck and lung. The previous fatality was an American student, Matthew Tassio, who was killed in 1995. Fifteen people have died at the Pamplona event over the past century.

The runs attract more than 2,000 people every morning of the nine-day fiesta. Many are young foreigners, drawn to an event made famous by Ernest Hemingway in his 1926 book The Sun Also Rises.

Local authorities warn that foreigners are more likely to injure themselves by drinking too much or indulging in other notoriously dangerous San Fermin rituals — such as drunken jumps off local monuments into the arms of people waiting below.

San Fermin kicks of Europe's festival season for tens of thousands of UK-based young Australians, New Zealanders and South Africans who tour the continent until the October beer festival in Munich.

While most runners survive unscathed, Pamplona's bulls all eventually meet a painful, frightening death. The six bulls that take part in each of the runs are later tormented and lanced in the city's bull ring during a regular bullfight. Most meet their death when a sequin-suited matador finally thrusts a sword into their neck.

Fugado was amongst the bulls due to be killed on Monday night.

The two British victims from Monday's run were being treated at the city's Navarra hospital. The 38-year-old American was gored slightly in the right calf muscle and was later released from the same hospital.

A second American and three Spaniards were also released after being treated for lighter wounds sustained during the adrenaline-fired run through the city's streets.