Spaniards went to the polls today in the first referendum on the European Union's new constitution, with supporters of the charter hoping europhile Spain will set a strong example for waverers in the bloc.
Prime Minister Jose Luis Rodriguez Zapatero has staked his reputation on making Spaniards, who joined the EU in 1986, the first to approve the document.
The "Yes" vote is expected to win easily, but low turnout would be a blow to Mr Zapatero's credibility after the opposition criticised him for rushing Spaniards to the polls.
Nearly 35 million voters were eligible to answer the question: "Do you approve the treaty establishing a constitution for Europe?" King Juan Carlos and Queen Sofia were among the first to vote after polls opened this morning.
By 5 p.m., around a third of Spaniards had cast their vote, just lagging participation at the same stage in last year's European Parliament election when final turnout was 46 per cent. Polling stations were due to close at 7 p.m.
"Today we are taking a decision of huge importance for the future of a united Europe. A very important decision for Spain, for its future and well-being," Mr Zapatero said after voting. "For that reason, I appeal to all citizens to participate."
Some 106,000 police were on alert for potential violence from the armed Basque separatist group ETA. On Thursday, police arrested a man and woman in Valencia with explosives for an "imminent" attack.
A survey by state pollster CIS showed around 90 per cent of Spaniards had little knowledge of the 350-page constitution after the brief campaign. Zapatero tried to focus the vote on the benefits of EU membership rather than the charter itself.