Hundreds of protesters battled police in the heart of Barcelona amid anger over the jailing of Catalan separatist leaders.
Masked protestors were seen blocking areas, damaging police vehicles, setting fire to large garbage bins, ransacking banks and attacking riot police officers with stones, cans and bottles.
Police responded with repeated volleys of foam bullets, smoke grenades, tear gas and water cannons.
The violence followed a largely peaceful demonstration that drew more than half a million people onto the streets of the Catalan capital.
Catalan interior affairs chief Miquel Buch distanced themselves from the riots, claiming "this kind of violence is unprecedented in Catalonia ... these people are not separatists".
Some 128 people have been arrested in the region over the past five days, with Spain's acting interior minister, Fernando Grande-Marlaska, warning that rioters faced up to six years in prison.
Hamas says it will hand over a Gaza hostage body
Hong Kong apartment fire toll hits 159, infant among dead
Sri Lankans sift mud to unearth victims four days after deadly cyclone
Hunt for missing flight MH370 to resume this month, Malaysia says
India revokes order to preload cybersecurity app on phones after outcry
