Thousands of people have crammed into the main square and adjacent narrow streets of Spain's Pamplona for the start of the famed San Fermin running of the bulls festival.

The fiesta, an uproarious blend of hair-raising daily bull runs and all-night partying, was immortalized in Ernest Hemingway's 1926 novel "The Sun Also Rises."

Revelers wearing traditional white outfits trimmed with red neckerchiefs and cummerbunds gathered for Sunday noon's launching of a firework rocket, which signals the beginning of the nine-day festival.

The regional government of Navarra said this year's festivities would be patrolled by 3,500 police to keep the adrenaline and alcohol-fueled events as safe as possible.

Animal rights activists protested Saturday, warning that 48 bulls are killed at the festival each year.