Twenty people were arrested, all foreigners, early on Thursday morning in Lloret de Mar following a street battle with police outside a discoteque.
The problem began at a disco, Colossos, in avenida Just Marlés when an electrical problem meant that there were insufficient generators to power the air conditioning. As a consequence, the disco doors were opened to allow some of the 1,800 people inside to get a breath of fresh air after several people fainted.
However, those who went outside for air were not let back in again and protests, then a riot began. Bottles were thrown, street furniture was vandalised and six police vehicles were damaged.
Nine riot squad officers and four other police officers were injured in the riots. Seven rioters required hospital treatment, either for cuts and bruises or alcohol intoxication.
The detainees are 13 French nationals, 3 Germans, 2 Dutch, 1 Swiss and 1 Slovenian.