Several thousand people have gathered in Barcelona in protest against an alleged excessive use of force by Spanish police during Catalonia's referendum on independence this weekend.

Tuesday's protest follows a call by Catalan trade unions for a general strike in Spain's northeastern region to condemn police violence, which left almost 900 injured, during Sunday's unauthorised vote.

Authorities said up to 50 roads in the region had been blocked as a result of the action, with bus and taxi services also having been affected.

Many businesses across Catalonia have closed for the day, with schools and medical centres also operating at minimal levels, if at all.

READ MORE: 'Yes' wins Catalonia independence vote marred by chaos

Carles Puigdemont, president of Catalonia's regional government, has offered his support to protesters.

"I am convinced this strike will be widely followed," he said on Tuesday.

A number of protests are scheduled to take place outside of polling stations where outbreaks of violence occurred between state officials and civilians participating in the referendum.

In Barcelona, the region's capital, public transport is expected to remain suspended for most of Tuesday.

Severe disruption

Port operations have also been severely disrupted, according to union officials.

Union spokespeople have said the widespread protest will "vigorously condemn" the police response to Sunday's poll, in which 90 percent of voters backed independence from Spain.

Mariano Rajoy, Spain's prime minister, defended police actions - which included the use of truncheons and shooting of rubber bullets - and praised officers for their "firmness and serenity" in upholding the rule of law.

The central government in Madrid said the vote, which had a 42 percent level of turnout, is illegal and contravenes the Spanish constitution.

Al Jazeera's Laurence Lee, reporting from Barcelona, said: "Many people are saying that the mandate, as they see it, of the referendum needs to be accepted and mirrored by the Catalan parliament. And they want their independence this week.

"If the Madrid government thought it was going to be able to crush the referendum and crush the Catalans on Sunday in the way it did with the police, then they misjudged it badly."

Spain's 1978 constitution decrees that the country is indivisible, and grants the national government exclusive power to hold referendums.

Catalonia's leaders appear intent on declaring independence from Spain in the coming days. Following the vote, Puigdemont said Catalonia had "won the right to an independent state".

Such a declaration, though lacking legal force, would present a historic constitutional challenge to Rajoy who has accused supporters of independence of trying to "blackmail ... the whole nation".