European Union (EU) leaders hailed Sunday Spain's overwhelming "yes" vote to the EU constitution, calling it a strong signal to other countries preparing to hold referendums on the historic text.

The welcome came after nearly four in five Spaniards backed the constitution, in the first of a series of national votes over the next 18 months or so, any one of which could in theory kill the document.

"The Spanish have said yes to Europe, yes to the future," said European Commission chief Jose Manuel Barroso, after speaking by telephone with Spanish Prime Minister Jose Luis Rodriguez Zapatero to congratulate him on the result.

"The Spanish people have sent a strong signal to their fellow citizens who will give their view on the constitution in the coming months," he added in a statement.

Almost half the EU's current 25 member countries are due to hold referendums on the constitution over the next 18 months or so, including countries with strong euroskeptic camps like Britain, Poland and the Czech Republic.

In principle the constitution, signed last October by EU leaders, has to be ratified by all EU states to come into force.

French President Jacques Chirac, who had travelled to Spain to support the "yes" campaign ahead of the vote, congratulated Zapatero on the result.

"This 'yes' from the Spanish people for the constitution and for Europe is a strong sign of and shows the way to other countries who will ratify this treaty in the months to come," Chirac said in a message released by his office.

Barroso trumpeted the need for the constitution, which is designed to streamline the expanding bloc's institutions and prevent decision-making gridlock as it grows to 27 or 28 members in the next few years and more beyond.

"The European Commission welcomes the very clear yes which Spain has given to a Europe which moves forward and which makes a difference," said the head of the EU's Brussels-based executive arm.

EU foreign policy chief Javier Solana echoed Barroso's words.

"I am convinced that the results in Spain will have a positive impact in consultations that will take place in other EU member states in the coming months," he said.

"This is an important step in the ratification process" of the constitution, whose "entry into force will make the EU stronger and more efficient. It will help the EU to fully assume its international responsiblities," said Solana.

According to final official results, the "yes" camp garnered 76.73 percent of votes. Turnout was 42.32 percent, or more than 14 million voters.

In Madrid, Zapatero also said his compatriots had shown their fellow EU citizens the way ahead.

"Our vote is a message to our fellow EU citizens who were awaiting our decision. Today Europe won, the EU constitution won, Spain won," Zapatero said. "We invite them to follow Spain's path", he added.