Media playback is unsupported on your device Media caption Police were filmed violently tackling voters and appearing to pull a woman by her hair

Nicola Sturgeon has said she was "increasingly concerned" about images from Catalonia as Spanish police tried to halt an independence referendum.

Police seized ballot papers at polling stations and fired rubber bullets during protests in Barcelona.

In a tweet the first minister said all should condemn the scenes "regardless of views on independence".

She said Spain should allow the poll which was declared illegal by the country's constitutional court.

And she called on the Spanish authorities to "change course before someone is seriously hurt".

Thousands of Catalan independence supporters occupied schools and other buildings designated as polling stations in order to keep them open.

In Girona, riot police smashed their way into a polling station where Catalan leader Carles Puigdemont was due to vote.

However, Mr Puigdemont was still able to cast his ballot at another polling station.

Catalan officials said more than 450 people had been injured

Meanwhile, the Spanish interior ministry said 12 police officers had been hurt and three people arrested.

It added that 92 polling stations had been closed.

Spain's deputy prime minister Soraya Saenz de Santamaria said police had "acted with professionalism and in a proportionate way".

Eyewitness - BBC political correspondent Niall O'Gallagher

I spent the morning at a school in central Barcelona which has been used as a polling station in today's referendum.

We visited the night before as locals prepared to stage an all-night sit-in to prevent the Spanish police from locking the doors.

When I returned, shortly before the polls were due to open, they had been joined by a crowd of hundreds determined that the vote go ahead.

There was no sign of the additional officers from the Guardia Civil and National Police forces who had been brought in from outside Catalonia to stop the vote.

Shortly before voting was due to begin the Catalan police, who had been observing without taking any action, appeared to leave, to applause from the would-be voters.

The atmosphere was tense as reports of Spanish police officers using force against nearby voters came through to those waiting in the rain.

People told me they were afraid and the vote was delayed as children and older people were moved away from the police's expected point of approach.

But that gave way when the first, elderly voters went through the school doors, emerging shortly afterwards to applause, some with tears in their eyes.

The government in Madrid has insisted it acted to protect Spanish democracy from an illegal and unconstitutional action by the authorities in Barcelona.

The larger question is whether Sunday's actions by the Spanish security forces will make previously sceptical Catalan voters ready to back independence for the first time.

Scottish Conservative leader Ruth Davidson also commented on events in Catalonia, urging dialogue to avoid violence.

She said: "Everyone will be shocked by the disturbing scenes coming from Catalonia. It is clear that this is a fast-moving situation, but we would urge the authorities to exercise restraint. Nobody wants to see people hurt.

"If the situation in Catalonia is to be resolved, the answer will come through dialogue and diplomacy, and not through violence."

The Scottish Greens called for the European Commission to investigate the behaviour of Spanish police

External affairs spokesman Ross Greer said: "The images coming out of Catalonia are deeply upsetting.

"To see Spanish police in full riot gear beating, throwing or firing rubber bullets at voters should be condemned without hesitation by any democrat.

"It's not for any of us to say whether or not Catalonia should be independent, but we should all stand up for the right of the Catalan people to decide their own future without being literally thrown from their polling stations by a brutal police force."