Pamplona: Thousands of thrill-seekers sprinted, skidded, and tumbled out of the path of a stampeding herd of bulls during the opening bull run of the San Fermín festival on Monday.

The high-adrenaline event marked the first of nine morning “encierros” (bull runs) held throughout the week-long celebrations in the northern Spanish city of Pamplona.

Led by six steers, the bulls charged through the city’s narrow, winding cobbled streets, covering the 846-metre (2,775-foot) course in just two to four minutes. Up to 4,000 runners take part in each daily run, many clad in the traditional white attire with red sashes and neckerchiefs.

Experienced Spanish runners often attempt to sprint just inches ahead of the bulls’ horns, taunting the animals with rolled-up newspapers in a heart-stopping display of daring.

Spectators lined balconies and wooden barricades along the route to watch the chaotic spectacle unfold, while millions more tuned in live on television across Spain and around the world.

The festival officially began on Sunday with the traditional chupinazo -- a firework launched from the town hall balcony -- signalling the start of festivities. Revelers then soaked each other in red and sparkling wine, a longstanding tradition.

While injuries are common during the runs, with participants frequently suffering bruises or being trampled in pile-ups, gorings also occur. On Monday, Spanish newspaper El País reported that several people were injured during the first run, though it was unclear if any had been gored.

According to unofficial records, at least 15 people have died in the bull runs since the early 20th century. The deadliest day was 13 July 1980, when four runners were killed by two bulls. The most recent fatality occurred in 2009.

Each afternoon, the same bulls that run through the streets are later killed in traditional bullfights in the city's arena, a practice that continues to provoke international criticism.

On Saturday, animal rights activists staged a protest in Pamplona ahead of the festival. Covered in fake blood and wearing plastic horns, they held placards declaring “Bullfights are a sin” and condemned the events as cruel and outdated.

Despite the controversy, the San Fermín festival remains one of Spain’s most iconic cultural celebrations, made famous internationally by Ernest Hemingway’s 1926 novel The Sun Also Rises, which follows a group of American expatriates drawn to the festival’s hedonism and spectacle.