Polling booths are now open in France in the first round of a bitterly fought presidential election that is crucial to the future of Europe.

Nearly 47 million voters will decide, under tight security, whether to back a pro-EU centrist newcomer, a scandal-ridden veteran conservative, a far-left admirer of Fidel Castro or a highly controversial woman who would shut borders and ditch the euro.

Adding uncertainty to France's most unpredictable election in decades, pollsters say they might not be able to give precise estimates of the outcome tonight because small and medium-sized polling stations will be open one hour longer than in past elections.

About 67,000 polling stations are being monitored by more than 50,000 police officers - because of the recent attack on the Champs Elysee.