Protesters in Barcelona have set fire to several cars during violent clashes with police.
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 claimed that projectiles had been fired at helicopters.
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 are protesting against jail sentences for nine leaders of a 2017 bid to declare the surrounding Catalonia region independent from Spain.
Spain’s prime minister warned that his government will not be provoked into overreacting.
In a televised address, Pedro Sánchez called on the pro-independence Catalan president, Quim Torra, to unequivocally condemn the use of violence.
Referring to the regional government’s unsuccessful attempts to secure independence, Sánchez added: “No leader can camouflage their failure behind curtains of smoke and fire.”