At least four streets were blocked by burning containers as people set bins and vehicles alight near the interior department of the regional government in the city.
Police also reported clashes in Girona, a town near the French border.
Officers fired foam bullets and charged towards protesters as tens of thousands took part in demonstrations on Wednesday evening.
Demonstrators threw rolls of toilet paper into the air to signify that “there is a lot that needs cleaning up”.
Some set up flaming barricades in the streets and hurled stones and firecrackers at officers.
Police said acid had also been thrown at them.
It is the third consecutive day of protests in the Catalan capital since the supreme court handed lengthy prison sentences to Catalan separatist leaders.
Nine separatists who led the 2017 bid for Catalan independence were jailed for between nine and 13 years.
Demonstrations began as peaceful protests on Monday but have since descended into violence.
Hundreds of police were on standby for further violence after more than 200 people were injured in clashes and 29 people were arrested on Tuesday.
Barcelona burns: Cars on fire during protests
The Spanish government says it will not rule out any measures to provide security in Catalonia.
However Spanish caretaker prime minister Pedro Sanchez said authorities will respond with “firmness, calmness and unity”.
He blamed “organised groups of extremists” for the unrest but said he would not be drawn into a game of an “ascending spiral of violence”.
Earlier on Wednesday, Mr Sanchez met other leaders in Madrid to address the trouble in Catalonia.
Some leaders wanted exceptional measures to be taken in the region.
Pete Ferrer, director of Catalonia’s regional police, said the street violence in recent days was “intolerable”.
“The situation is very, very difficult, but the police have the means they need to deal with it,” he said.
Further protests are planned in the coming days as separatists vow to continue pushing for independence.
About half of the region’s 7.5 million residents support Catalonia’s independence.
