At least two runners were injured during the third bull run at Pamplona’s traditional Festival of San Fermin in northern Spain.

Dressed in white clothes and red scarves as per tradition, thousands of people filled the Pamplona City Hall square to attend the “chupinazo” – the launch of a massive firecracker – marking the start of the nine-day festival on Saturday.

The run became world famous after being immortalised by American writer Ernest Hemingway in his novel The Sun Also Rises in 1926.

Pamplona is awash with red and white. The San Fermin festivities, with medieval origins from the 16th century, also includes concerts, religious processions, and lots of wine.

The climax, however, comes every day at 8am when hundreds of participants launch themselves into a dangerous race with six heavy fighting bulls, some weighing more than 600kg (1,320 pounds), through the narrow streets of the city centre.

During the intense “running of the bulls”, which lasts less than three minutes, the runners try to get as close as possible to the beasts in their sprint to the Pamplona bullring, where bullfights are held in the afternoon and the animals are killed by matadors.

Six people were hurt on Sunday with one participant gored and five suffering bruising. There have been 16 deaths since 1924, the last in 2009.

Animal rights activists call the bull runs “medieval cruelty” and say they must be halted immediately. The bull run is nothing more than panicked animals trying to escape through crowds of people screaming, they say.