French voters on Sunday will choose their next president after an unpredictable campaign that has divided the country, the media reported.
The second round contest pits centrist Emmanuel Macron, a 39-year-old former investment banker, against the far-right nationalist Marine Le Pen, 48, the BBC reported.
Citizens in some overseas territories and many French expats abroad have begun voting.
The polls open in metropolitan France at 8 a.m. and will close at 7 p.m.
Polling stations will remain open in some big cities until 8 p.m., with early estimates of the result due to be reported immediately after they close.
The two candidates, who topped a field of 11 presidential hopefuls in the first round election on April 23, have offered voters starkly different visions of France, reports the BBC.
Macron, a liberal centrist, is pro-business and a strong supporter of the European Union (EU), while Le Pen campaigned on a France-first, anti-immigration programme.
She wants France to abandon the euro in the domestic economy, and hold a referendum on France's EU membership.
Macron is widely expected to win the vote, but analysts have said high abstention rates could damage his chances.