Spanish police have clashed with voters as thousands of people flocked to the polls to vote in the Catalonia independence referendum.

Catalan emergency services said 38 people were hurt, mostly with minor injuries, as a result of police action.

The country's national police began to seize ballot boxes and voting papers from Catalan polling stations on Sunday morning.

Voters also described the police as "aggressive" and giving "no warning" as hundreds of would-be voters were forcefully removed.

Daniel Riano, 54, was at the Estela school in Barcelona when the police pushed aside a large group gathered outside.

"We were waiting inside to vote when the National Police used force to enter, they used a mace to break in the glass door and they took everything."

He said that "one policeman put me in a headlock to drag me out, while I was holding my wife's hand. It was incredible. They didn't give any warning".

Ferran Miralles said a crowd scuffled with police outside as they formed a tight perimeter around the door.

They said "they were very aggressive. They pushed me out of the way."

A Spanish National Police officer aims a rubber-bullet rifle at pro-referendum supporters in Barcelona (AP)

Elsewhere in Barcelona, police have detained several people outside the Treball voting centre amid scuffles on the street. Officers dragged some of the protesters away and detained them.

At a polling station, due to be used by the Catalan president Carles Puigdemont in Sant Julia de Ramis, riot police used a hammer to smash the glass of the front door and lock cutters to force their way in.

Scuffles erupted outside between police and people waiting to vote with at least one woman injured and wheeled away on a stretcher by paramedics.

In a statement referencing the police action a senior Spanish government official told Reuters: "We have been made to do something we did not want to do."

Riot police also clashed with voters outside a Barcelona voting station, where dozens of police used riot shields to push people back, a Reuters witness said.

(Getty Images) Riot police clash with voters at polling stations across Catalonia (Getty)

People waiting to vote chanted "we are people of peace" and "we are not afraid".

The Catalan leader Carles Puigdemonnt cast his ballot in the village of Cornella del Terri instead.

Leading up to the referendum, Spanish police arrested Catalan officials, seized campaigning leaflets, sealed off many of the 2,300 schools designated as polling stations and occupied the Catalan government's communications hub.

The Catalonian regional government is attempting to make it easier for people to vote following the closures.

It said people can vote at any polling station if their designated one is closed and voting slips printed at home would also be accepted.

Catalonia independence referendum: Riot police clash with voters Show all 17 1 /17 Catalonia independence referendum: Riot police clash with voters Catalonia independence referendum: Riot police clash with voters A man faces off Spanish Civil Guards outside a polling station in Sant Julia de Ramis Reuters Catalonia independence referendum: Riot police clash with voters Riot police form a security cordon around the Ramon Llull school in Barcelona EPA Catalonia independence referendum: Riot police clash with voters Riot police evict a young woman during clashes between people gathered outside the Ramon Llull school in Barcelona EPA Catalonia independence referendum: Riot police clash with voters Spanish Civil Guard officers break through a door at a polling station in Sant Julia de Ramis Reuters Catalonia independence referendum: Riot police clash with voters Spanish National Police clash with pro-referendum supporters in Barcelona on Sunday AP Catalonia independence referendum: Riot police clash with voters Crowds raise their arms up as police move in on members of the public gathered outside to prevent them from voting in the referendum at a polling station where the President Carles Puigdemunt will vote later today Getty Catalonia independence referendum: Riot police clash with voters People confront Spanish Civil Guard officers outside a polling station Reuters Catalonia independence referendum: Riot police clash with voters Three man hold each other as they try to block a Spanish police van from approaching a polling station AP Catalonia independence referendum: Riot police clash with voters A woman shows a ballot to a Spanish Civil Guard officer outside a polling station Reuters Catalonia independence referendum: Riot police clash with voters A man wearing a shirt with an Estelada (Catalan separatist flag) and holding carnations faces off with a Spanish Civil Guard officer Reuters Catalonia independence referendum: Riot police clash with voters Police try to control the area as people attempt to cast their ballot at a polling station in Barcelona Getty Catalonia independence referendum: Riot police clash with voters A man is grabbed by officers as police move in on the crowds Catalonia independence referendum: Riot police clash with voters Two women argue with a Spanish National policeman during clashes between Catalan pro-independence people and police forces at the Sant Julia de Ramis sports centre in Girona EPA Catalonia independence referendum: Riot police clash with voters Sant Julia De Ramis in Spain Getty Catalonia independence referendum: Riot police clash with voters Confrontation outside a polling station in Barcelona, where police have tried to stop people voting AFP/Getty Images Catalonia independence referendum: Riot police clash with voters A Spanish National Police officer aims a rubber-bullet rifle at pro-referendum supporters in Barcelona AP Catalonia independence referendum: Riot police clash with voters Riot police clashed with voters as polls opened in Barcelona Sky News

Seventy-three per cent of polling stations have been able to open, Catalan government spokesman Jordi Turull has announced.

He asked for patience, saying “there are constant attacks on the computer system”.

The ballot papers contain one question: "Do you want Catalonia to become an independent state in the form of a republic?" with two boxes: Yes or No.

Spain's Constitutional Court ordered the vote to be suspended and central authorities say it is illegal.

Regional separatist leaders have pledged to hold it anyway, promising to declare independence if the "yes" side wins, and have called on 5.3 million eligible voters to cast ballots.