France, March 22 -- Heading nearly 35,000 municipalities - from major cities to villages with only a few dozen residents - mayors are France's most trusted elected officials.

Most mayors were elected outright in the first round on 15 March, having won more than 50 percent of the vote.

But there are runoffs on Sunday in around 1,590 constituences, including France's biggest cities.

Some 17 million people are eligible to vote.

Key battle grounds include Paris, Marseille, Lyon, Bordeaux and Toulouse.

The local ballots are being closely watched to gauge the mood on the ground and potential party alliances before the election of a successor to centrist President Emmanuel Macron next year. 

Voting started at 8 a.m. and ends...