An American tourist was gored in the abdomen on the third day of the centuries-old annual bull-running festival in the northern Spanish town of Pamplona on Wednesday, organisers said.

The 22-year-old man from California was stable after being admitted to hospital along with a Greek man, aged 20, who suffered facial injuries.

Several of the hundreds who took part were trampled by bulls, but were not reported to require treatment.

Wednesday's injuries added to 13 people treated after the first early morning run on Monday, including a 37-year-old man who suffered a collapsed lung, ruptured spleen and broken ribs.

The San Fermin festival draws tourists from around the world, who don traditional all-white garb with a red sash around the waist and red kerchief around the neck before running through narrow, twisting cobbled streets, pursued by bulls.

The chase lasts about four minutes and is shown live on television. The bulls are usually killed after the runs by bullfighters.

The festival dates back to the 13th century. The bull-running was made famous by Ernest Hemingway's novel "The Sun also Rises", a semi-autobiographical account of an alcohol-fuelled visit to the festival by a group of squabbling British and American friends in the 1920s.