​Catalans started to form queues early on Sunday morning as they sought to defy Spanish authorities by voting in a banned independence referendum that has raised fears of unrest in the wealthy northeastern region.

The referendum, declared illegal by Spain’s central government, has thrown the country into its worst constitutional crisis in decades and raised fears of street violence as a test of will between Madrid and Barcelona plays out.

Civil Guard national police reinforcements also began deploying in the pre-dawn darkness in Barcelona where about 100 police vans streamed into the capital of Catalonia from the port where they had been stationed, a Reuters witness said.

“I have got up early because my country needs me,” said Eulalia Espinal I Tarro, a 65-year-old pensioner who started queuing with around 100 others outside one polling station, a Barcelona school, at 5 a.m. local time, four hours before the scheduled start of voting.

“We don’t know what’s going to happen but we have to be here.”

People gather outside a school assigned to be a polling station by the Catalan government at the Gracia neighbourhood in Barcelona early Sunday. (Bob Edme/Associated Press)

Leading up to the referendum, Spanish police have 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.

But Catalan leaders, backed by pro-independence supporters, have refused to abandon their plans. Families have occupied scores of schools earmarked as voting centres, sleeping overnight in an attempt to prevent police from sealing them off.

Pro-independence Catalan leader Carles Puigdemont originally said that if the Yes vote won, the Catalan government would declare independence within 48 hours, but regional leaders have since acknowledged Madrid’s crackdown has undermined the vote.

The Madrid government, which has sent thousands of police to Catalonia to enforce a court ban on the vote, believes it has done enough to prevent any meaningful referendum taking place.

People are seein at the Miquel Tarradell school, assigned to be a polling station by the Catalan government, early Sunday. (Manu Fernandez/Associated Press)

Farmers have used tractors to guard polling stations in 30 Catalan towns, according to Spanish media reports. They included one at a sports centre in Sant Julia de Ramis, near Girona, where Puigdemont was scheduled to vote later.

At other polling centres, activists carried away schools’ iron gates to make it harder to seal them off.

Organizers had asked voters to turn out early and for “massive” crowds to be lined up waiting to vote by 7.30 a.m., hoping for this to be the world’s first image of voting day.

A minority of around 40 per cent of Catalans support independence, polls show, although a majority want to hold a referendum on the issue. The region of 7.5 million people has an economy larger than that of Portugal.