Supporters of Catalan independence began occupying polling stations on Friday, setting up a possible confrontation with police who have been ordered to clear them out by Sunday morning to ensure a referendum cannot go ahead.

The central government, which has sent thousands of police reinforcements to stop people voting and has attempted to dismantle the infrastructure needed to conduct the referendum it says is illegal, insisted it would not go ahead.

Catalan leader Carles Puigdemont told Reuters in an interview, however: "Everything is prepared at the more than 2,000 voting points so they have ballot boxes and voting slips, and have everything people need to express their opinion."

Bands played at a closing rally for the referendum campaign in Barcelona where people constructed the slogan "Referendum is democracy" in big white letters on a stage in front of a cheering crowd, many draped in the red-and-yellow Catalan flag.

People preparing to camp out in polling stations in order to defy court orders to close them were also in high spirits. At one Barcelona school, Hector, a 43-year-old local, said five or six families would be spending the night.

"We want to make sure the school is open for activities and at night when they might come to clear us out or empty it, there will be families sleeping or people in the street," he said, adding that they planned to play ping-pong and cook a fideua seafood dish on Saturday.

The head of the Catalan regional police ordered officers to evacuate and close polling stations by 6 a.m. on Sunday, before the voting is due to open at 9 a.m.

In an internal memo published by La Vanguardia newspaper, the police chief said force should be used only as a last resort.

"At all times, before using force, you must take into account what might be the consequences of this police action and avoid the escalation of this situation, especially when there are children, elderly or other vulnerable people amongst the crowd," the document, whose authenticity was confirmed by a police spokeswoman, said.

"PEACEFUL RESISTANCE"

So far, the Catalan police, known as the Mossos, a force that is held in affection in the region, particularly after the Islamist attacks in August, have shown a friendly face.

"The Mossos have come to see what we are doing and they've seen we're having a party," said 45-year-old Ferran Taberner who was at the school with his daughter. "If it gets complicated we'll stay inside peacefully and they won't move us."

Organisers said 60,000 people had registered to participate in the mass school sleepover which they say will show "peaceful resistance", even if they are prevented from voting.

"I don't believe there will be anyone who will use violence or who will want to provoke violence that will tarnish the irreproachable image of the Catalan independence movement as pacifist," Puigdemont said.

At a news conference, regional officials displayed one of the white plastic ballot boxes bearing the crest of the regional government. Puigdemont has said more than 6,000 were being kept in a secret place.

Police have confiscated thousands of voting slips, and courts have fined and threatened to arrest regional officials.

Catalonia's High Court ordered Google to delete a smartphone application that the Catalan government was using to spread information about the vote. A company spokeswoman said Google removes content when it receives a court order.

Madrid, which claims the authority of a constitution that declares the country to be indivisible, remained implacably opposed to the vote, but also expressed the hope Sunday would be peaceful.

"I insist that there will be no referendum on Oct. 1," government spokesman Inigo Mendez de Vigo said, adding that organisers would face criminal charges for trying to hold it.

In a sign that large crowds are expected on the streets on Sunday, department store chain El Corte Ingles said it would shut three stores in central Barcelona. The central government said airspace above the city would be partly restricted.

Credit rating agency S&P said that while it did not it expect Catalonia, a wealthy region that borders France, to secede from Spain, protracted tensions between Madrid and Barcelona could have a negative impact on the country's economic growth outlook.