Barcelona (AFP) - Demonstrators hit the streets of Barcelona on Friday for a third day of protests against the Spanish authorities' crackdown on preparations for a banned independence referendum in Catalonia that has divided the region.

Some 2,000 people, many draped in red and yellow Catalan independence flags, gathered outside a court on the outskirts of Barcelona where six Catalan government officials, who were detained on Wednesday, were summoned for questioning.

"I see the detentions as a violation of human rights. It's unheard of. For me we have returned to the Franco era," said one demonstrator, 60-year-old Josep Esteve.

Drivers honked in support of the protesters as they passed by, prompting applause from the demonstrators. Some of those gathered called for a general strike.

The six Catalan government officials inside the court -- under investigation for alleged crimes of disobedience, embezzlement and prevarication -- refused to answer questions.

The presiding judge ordered their provisional release, though they will have to appear weekly before the court while the probe continues.

Elsewhere, demonstrators gathered outside Barcelona's High Court in the heart of the city, where dozens of people had camped overnight in tents while hundreds of students occupied the patio of the University of Barcelona.

Catalan vice president Oriol Junqueras has said that the arrest of 14 Catalan government officials on Wednesday and the seizure of nearly 10 million ballot papers for the referendum had dealt a blow to the preparations for the vote slated for October 1.

But is has also inflamed the passions of supporters of independence.

"I don't know if they see it, but any action which they take is a real boomerang against them," Catalan government spokesman Jordi Turull told a news conference.

- Sedition -

Catalonia's regional government insists the referendum -- deemed illegal by Madrid -- will go ahead despite the crackdown and a ruling suspending the vote from Spain's Constitutional court.

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"Sorry, Spain. Catalonia is voting on independence whether you like it or not," read the headline of an opinion piece defending the vote by Catalonia's President Carles Puigdemont published in the Washington Post.

Spanish authorities continued their efforts to block the referendum in the wealthy northeastern region of Spain which is home to roughly 7.5 million people.

Spain's Guardia Civil police searched a cardboard packaging company in the town of Odena near Madrid but found no material that could be used in the vote, a spokesman for the police force said.

Spanish public prosecutors meanwhile pushed for possible sedition charges against leaders of protests in Barcelona on Wednesday that saw officers surrounded for several hours and three police vehicles destroyed.

- Police reinforcements -

Spain's Interior Minister Juan Ignacio Zoido sent a letter to the Catalan government warning the Madrid was sending extra police to Catalonia who "will act if the illegal referendum is held".

The ministry has chartered three cruise ships with a capacity for 6,600 passengers to house the officers.

Two of the ships are moored in the port of Barcelona while another is in Tarragona, some 100 kilometres (60 miles) south of the Catalan capital.

Madrid has not said how many extra police from the national police force and the Guardia Civil force would be sent but government spokesman Inigo Mendez de Vigo said they would "reinforce and support" Catalonia's regional police force, the Mossos d'Esquadra.

He accused the pro-separatist camp of "harassing" of those opposed to the referendum.

"They pressure offices of the (ruling) Popular Party that wants to respect the law, they have pressured school directors, university rectors, public workers, journalists, newspapers."

A group of 47 mostly far-left European Union lawmakers -- out of the 700 in the European parliament -- sent a letter to Spanish Prime Minister Mariano Rajoy urging accusing him of imposing a "state of siege" in Catalonia -- mirroring the language of the Catalan government.

Polls show Catalans are sharply divided on whether they want independence or not, with the latest survey in July showing 49.4 percent against and 41.1 percent in favour.

Despite the divisions, a large majority of Catalans want to vote in a legitimate referendum to settle the matter.