France has overwhelmingly rejected the EU Constitution, creating political uncertainty for the bloc and for the future of the constitution.
The French Interior Ministry said that with 85% of votes counted, the No camp had 56% of the vote compared to 44% for Yes.
Opponents of the constitution began celebrating in Paris's central Place de la Bastille as soon as the first exit polls appeared.
President Jacques Chirac said he had taken note of the rejection decision.
He gave no indication of his future intentions, but said France and the EU must answer the vote by unifying.
He said France's ambitions were tied to Europe and he would make a decision on his government in the coming days.
The French Defence Minister, Michele Alliot-Marie, said rejection was 'a defeat for France and a defeat for Europe'.
Reacting to the result, former EU Commission President, Romano Prodi, said he was 'enormously disappointed' with France's rejection, adding that Europe needed to listen to the signal sent by French voters.
Jack Straw, the British Foreign Secretary, claimed France's rejection of the constitution raised profound questions about the future of the bloc and should be followed by a period of reflection.
In advance of a referendum on 1 June, the Dutch Prime Minister Jan Peter Balkenende renewed an appeal to Dutch voters to approve the constitution despite the French rejection.
Analysts have predicted that turnout in the Dutch referendum on Wednesday is likely to be much lower now that France has rejected the treaty.
Polls taken before the French vote showed that a majority of Dutch are also against the constitution.
Polling in France began at 8am this morning and turnout was estimated to be 75%.
The French Interior Ministry said turnout was greater than it was in 1992 during the referendum on the Maastricht Treaty.
The referendum became the most intensely fought campaign in French history.
Supporters of the constitution said it would ensure France's influence at the heart of Europe.
The No camp, which had been topping polls in the run-up to the referendum, argued it would undermine the country's ability to protect jobs and wages.
