An anti-establishment movement is the favourite to win as voters head to the polls to pick a new mayor in Rome.

The election is one among a handful of town hall contests across Italy on Sunday that will test the prime minister's governing Democratic Party.

A broad corruption scandal and deteriorating public services have turned many voters against traditional parties in Rome, driving support to the grassroots, populist 5-Star movement. Local elections will also be held in Milan, Naples and Bologna.

While prime minister Matteo Renzi could emerge weaker from the races, which take into account one-quarter of Italy's voting population, analysts say the real barometer will be a referendum on constitutional changes launched by his government and heading to a vote in the autumn.

Run-offs are expected on June 19 in most contests, unless candidates manage to win more than 50% of the vote, which is rare in the first round.

The capital race is the most volatile. A victory for 5-Star candidate Virginia Raggi would mark the biggest administrative victory for the movement founded by comedian-turned-political leader Beppe Grillo. It would also be the first time a woman would run the eternal city.

Rome has been run by a government-appointed commissioner after the last mayor, a political outsider, lost support of the Democratic Party-dominated city council amid controversy over his expenses.

In Milan, the race pits two centrist managers as the front-runners, with the former manager of Expo 2015, Giuseppe Sala, running as the Democratic Party candidate against former city manager Stefano Parisi with broad centre-right backing.