Wednesday night's protests are described by a police source to La Vanguardia as more serious than yesterday's.
In Lleida in the northwestern part of Catalonia, protesters have set fire to containers near the prison where the rapper Pablo Hasél has been taken.
Tear gas and rubber bullets
Several media outlets report that tear gas and rubber bullets have been fired at protesters in Madrid and Barcelona.
In the Plaza del Sol, the protests are said to have started calmly but then escalated and led to skirmishes between police and protesters, writes Reuters.
Similar reports come from Barcelona where a Reuters reporter is said to have been injured in the riots.
Convicted of glorifying terrorism
On Tuesday, 18 people were arrested.
55 people were injured, 25 of them were from the police.
According to the news agency AP, at least 30 people were arrested during Wednesday's protests.
The protesters are protesting against the arrest of, and the verdict against, the rapper Pablo Hasél, who in 2018 was convicted of glorifying terrorism and insulting the royal family because of what he wrote on Twitter but also in lyrics.
On Monday, Hasél was arrested in Lleida after the deadline to surrender to serve a nine-month prison sentence expired.