Another 12 people were hurt and 16 arrested in clashes early on Saturday between police and street drinkers in the historic city of Salamanca, 180km northwest of Madrid, state radio said.
Tens of thousands of young people congregated in cities around Spain on Friday night in an attempt to hold the country's biggest street drinking session or "botellon" (big bottle).
In Barcelona, the event degenerated into pitched battles between police and drinkers in the narrow old streets of the city centre that lasted most of the night.
The riot began after midnight when youths began throwing bottles and cans at police who responded with baton charges and fired rubber bullets, according to media reports.
Firemen were called to put out 50 blazes as the youths set fire to bins. Shop windows were broken and several shops ransacked, media reports said.
A spokesman for Barcelona municipal police blamed the disturbances on about 200 people who he said were out to cause trouble. He said the 68 injured included 37 police officers.
Drinking the night away
The botellon has become part of city life in Spain in recent years as teenagers, bored at home and too poor to go to bars, buy beer, spirits and cartons of wine from food stores and lounge around in plazas, drinking throughout the night.
Bombarded with noise, the stench of urine and vomit on the streets, many city councils brought in rules to ban drinking on the street.
Spain is recovering from its
biggest botellon yet
Police now patrol many botellon spots at weekends, moving along groups of teenagers who mix cocktails with cheap spirits or "calimocho" - red wine and cola.
Youths rallied revellers by email and SMS messages for "macrobotellones" in 20 cities around Spain on Friday, while authorities pleaded with parents to keep their children under control and warned them of the danger of under-age drinking.
Heavy rain put a dampener on the events in several cities on Friday, while in Madrid a tight police cordon around central squares discouraged drinkers.
Some city authorities, such as those in Seville, Granada and Valladolid, allowed the gatherings to take place in designated areas, and up to 25,000 people gathered in the southern city of Granada.
A police spokesman said: "We've never seen anything like this in Granada. There's no doubt that this is the biggest botellon in Spain."