Hundreds of thousands of people have taken to the streets in Barcelona and Madrid this weekend to protest for – and against – the Catalan government’s push for secession from the rest of Spain.

In Madrid, a small group of protesters rallying under the slogan “for the unity of Spain” appeared to be flashing fascist salutes in a procession led by a group aligning themselves with far-right party Falange Española‏ de las Jons, which held power during the Francoist dictatorship period of the country.

Use of the salute is illegal in some countries. In Germany, Slovakia and Austria, the gesture is considered a criminal offence, while in countries like Canada and France, it is viewed as hate speech if used for disseminating Nazi ideology.

The rallies come a week after Catalan leader Carles Puigdemont and other separatist leaders of the Catalan government held a referendum on secession that the Spanish government branded illegal.

The “Yes” side won the referendum by a landslide, winning 90 per cent of the vote, though less than half of the region’s electorate cast their ballots.

Protesters on Sunday called for the imprisonment of Mr Puigdemont after he pledged to push for independence.

Demostrators in Spain against tomorrow's Catalan vote sing Francoist songs while making the fascist salute. pic.twitter.com/7faYijvBTP — Andrés Boix Palop (@Andres_Boix) September 30, 2017

The Catalan leader is set to address the regional parliament on Tuesday “to report on the current political situation”.

Meanwhile, Spanish Prime Minister Mariano Rajoy has vowed that his government will not allow Catalonia to separate from the rest of the country.

In an interview with Spanish newspaper El Pais, Mr Rajoy said he will consider employing any measure “allowed by the law” to stop the region’s separatists.

He said that also includes bringing Article 155 of the Spanish Constitution into effect, which allows the central government to take control of the governance of a region “if the regional government does not comply with the obligations of the Constitution”.

Protesters appear to raise their arms in fascist salutes at a rally in Salvador Dali Square in Madrid (Getty)

“The ideal situation would be that I don’t have to find drastic solutions,” he said. “But for that to happen there will have to be some rectifications.”

On Sunday, Barcelona police estimated as many as 350,000 people participated in a rally organised in the Spanish city. Event organisers, however, claimed the number was much higher, asserting there were at least 950,000 attendees.

People raise their hands painted in white, to symbolise they are in favour of talks, in Sant Jaume Square in Barcelona (AP)

Many protesters in Barcelona have called on Mr Rajoy and Mr Puigdemont to negotiate and find a solution to what has been widely regarded as Spain’s worst political crisis in nearly four decades.

Those who are opposed to Catalonia’s secession hope recent pressure from banks and major businesses will discourage Catalan leaders from attempting to separate.

A number of businesses, including Catalonia’s top two banks have announced plans to relocate their headquarters to other parts of Spain, while others have raised concerns over losing European Union membership and access to its common market in the event of secession.