PARIS, April 23 (Xinhua) -- French voters began casting their ballots Sunday morning in the first round of a historic presidential election that will weigh on the future of Europe.

The voting will winnow down a list of 11 candidates to two finalists for a runoff vote scheduled for May 7, if no one wins by at least 50 percent in the first round.

Polling stations at France's European continent opened at 8 a.m. (0600 GMT) and will run for a maximum of 12 hours. Those in the largest cities will close at 8 p.m. (1800 GMT). In France's overseas territories, the voting was held on Saturday.

Around 47 million French voters are registered to cast their votes at some 69,000 polling stations.

Security measures have been tightened after a number of incidents occurred in the week running up to the voting day, including Thursday's shooting in the Champs-Elysee avenue which left one police officer killed and two others injured.

Police officers and gendarmes were seen carrying out identification and security checks at the entrances of some polling stations.

French Prime Minister Bernard Cazeneuve has pledged to mobilize "all right means" to safeguard the election, including the deployment of 50,000 police officers and gendarmes.

Out of the 11 candidates, four remain frontrunners in previous polls, namely the centrist former Minister of economy Emmanuel Macron, the far-rightist Marine Le Pen, the right-wing conservative Francois Fillon and the far-leftist Jean-Luc Melenchon.