Demonstrators faced off with Barcelona police on the sixth consecutive night of protests in support of a controversial rapper jailed over incendiary tweets.

While a group of masked protesters threw bottles, firecrackers and other missiles at officers guarding Barcelona's police headquarters, last night's rally was calmer than on previous nights, when the demonstrations escalated into violent clashes.

Shouting "Freedom for Pablo Hasel", several hundred people gathered under a heavy police presence in front of the main train station before marching into the city centre.

Some protesters set up barricades on the city's Las Ramblas boulevard and lobbed objects at police, with at least five people arrested for smashing the windows of a clothing store and injuring an officer, police said on Twitter.

More than 100 people have been arrested in Barcelona and other cities in Spain's northern Catalan region since Tuesday, when angry demonstrations erupted after police detained Mr Hasel, 32, and took him to jail to start serving a nine-month sentence in a highly contentious free speech case. 

Saturday's unrest saw protesters smash their way into shops along Barcelona's glitzy Passeig de Gracia shopping avenue, looting stores such as Nike, Versace, Tommy Hilfiger, Hugo Boss and Diesel. 

Known for his hard-left views, Hasel was handed a nine-month sentence over tweets glorifying terrorism and videos inciting violence.

Catalan local police Pablo Hasel at Lleida University earlier this month

The court ruling said freedom of expression could not be used "as a 'blank cheque' to praise the perpetrators of terrorism".

He was also fined about €30,000 for insults, libel and slander for tweets likening former king Juan Carlos I to a mafia boss and accusing police of torturing and killing demonstrators and migrants.

His case has become a cause celebre among campaigners, who say that jailing him is a disproportionate response and a dangerous assault on free speech.