An Australian suffered injuries to a thigh and three other people were slightly hurt Saturday as thousands of Spaniards and tourists celebrated the start of the nine-day San Fermin bullrun.
The festival involves copious amounts of dancing, alcohol and the "encierro", when bulls are released onto the streets and hundreds of people are chased along an 825-metre (yard) course leading to the arenas where bullfights are later staged.
Fourteen people have died in the event since 1911.
On Saturday high attendance delayed the start of the run which normally begins at 8:00 am sharp for five minutes. Experts quoted by Spanish television said that it was not very fast either.
Several bulls and runners slipped and fell on the cobblestoned street.
The festival officially began Friday night with the lighting of the traditional chupinazo cracker by Pamplona's mayor.
Organisers expect more than one million people, many of them from Britain.
The bullrun has been criticised by international animal rights group PETA (People for the Ethical Treatment of Animals) for what it says amounts to gratuitous cruelty.