Television pictures showed a chaotic pile of fallen runners blocking the entrance to the bullring in the town, the end point of the frantic dash through the cobbled streets.
The pile-up blocked several of the half-tonne bulls from reaching the arena, causing chaos as runners tried to pull fallen companions free, while some of the bulls leapt over the pile, crushing runners under their hooves.
One man was seen being carried away unconscious by emergency workers, bleeding from the face as an anxious companion, dressed in the traditional white shirt and red neckerchief of the festival, looked on.