Catalonia's vice-president said more than six out of ten voters are expected to take part in the poll despite the crackdown from Madrid.
Oriol Junqueras said Catalan citizens will be able to vote "even if somebody takes voting stations by assault and tries to avoid something as natural as placing a voting slip in a ballot".
Catalan authorities say they will declare independence within 48 hours after announcing the vote's results if the yes side wins.
On Thursday over 80,000 students took part in a march through Barcelona.
Socialist Worker photographer Guy Smallman who is in Barcelona, reports, “Most of those whom we spoke to said the same thing. This popular uprising is not about Catalan nationalism.
“All agree that the real issue is democracy and a creeping feeling that the undemocratic structures of the Franco regime were never properly dismantled and still suppress the Spanish people.
“This has been brought into sharp focus by the austerity imposed in recent years combined with the banning of this vote and the drafting in of several thousand riot police to try and halt the referendum on Sunday.
“Right now it is illegal to even put up posters about the vote, but this is being openly defied by people of all ages and political persuasions.
“Outside the main university a row of tables stretches down the street as striking student volunteers hand out voting forms and information to queues of local people.
Today, Friday, agricultural trade unions and cooperatives organised a huge convoy through the centre of Barcelona.
Guy says, “Hundreds of students greeted the farmers and workers as the motorcade passed the main university. The police were nowhere to be seen with the exception of some local traffic cops whom politely facilitated the procession as it went through the city centre.”
The referendum is due to take place on Sunday. Activists started distributing ballot papers, handing out one million in a day.
The Tory government of the Spanish state, headed by prime minister Mariano Rajoy, is gambling that its hard line against allowing a referendum will play well in other parts of Spain.
It was Rajoy’s party that in 2010 blocked in court a deal agreed by the parliaments in Madrid and Barcelona to implement further autonomy.
Last week the paramilitary Civil Guard seized ten million ballot papers, and around 1.5 million pro-referendum leaflets, posters and printing materials.
The Spanish ministry of finance blocked all bank accounts held by the Catalan government.
The Constitutional Court has announced that 24 referendum organisers will be fined up to £10,700 a day until they abandon preparations for the vote.
But the response has been huge.
Hundreds of thousands of people have taken to the streets of Barcelona against the state crackdown and for the right to vote.
Dockers in Barcelona decided at a mass meeting not to work on ships brought in to house officers and vehicles from the Spanish National Police and the Civil Guard.
Dockers in Tarragona have also said they will not work on police ships.
The Catalan CGT, a trade union grouping of some tens of thousands, released a statement. “After discussions with other unions, we have submitted the call for a general strike starting on 3 October,” it said.
It’s right to fight for democratic rights. And doing it through mass protests and strikes can flow over into a wider struggle against the minority government and its austerity programme.