The firing of the traditional "chupinazo" rocket here Saturday before a giant crowd marked the start of the nine-day San Fermin festival.

The inauguration ceremony normally takes place at midday on July 6 in this northern Spanish city but it had to be postponed for about 15 minutes due to the unexpected unfurling of a giant Basque flag in front of the mayor's house.

Authorities said the flag could prevent the safe firing of the rocket from the city hall's balcony and needed to be removed beforehand.

Pamplona Mayor Enrique Maya expressed his "indignation" over the incident, although authorities said no arrests had been made.

The "chupinazo" marks the start of nine days of revelry on the streets of Pamplona, a normally quiet town that receives hundreds of thousands of Spanish and international visitors annually during the event.

The San Fermin festival is best known for its eight running of the bulls, which take place each morning beginning at 8:00 a.m. from July 7 until July 14.

The tension- and emotion-filled runs are dangerous because some people take part in them after all-night drinking binges, which make them reckless and more likely to get too close to animals that weigh in excess of 500 kilos (1,100 pounds).

Hundreds of other folkloric events also have been scheduled for this edition of the festival. EFE