Polling stations opened in mainland France at 0600 GMT Sunday, May 6, a day after voting got under way in France's overseas territories.

Preliminary results are expected around 1800 GMT (2 am EDT), AP reports.

The run-off election could see Socialist challenger Francois Hollande defeat incumbent Nicolas Sarkozy by capitalizing on public anger over the government's austerity policies.

Hollande beat Sarkozy by about half a million votes in the first round of voting on April 22, which saw 10 candidates competing for the job of running this nuclear-armed country with a permanent seat on the UN Security Council for the next five years.

The first round turnout of around 80 percent was higher than expected and is being closely watched again, with polls suggesting Sarkozy's best chance of an upset comes from even greater voter turnout Sunday.