Senior executives of Italy's biggest motorway operator made an early exit from a ceremony held to remember victims of a deadly bridge collapse in the port city of Genoa, after some grieving relatives asked for them to leave.

The chief executive and chairman of infrastructure group Atlantia, which operated the bridge that collapsed on 14 August last year, and other company officials left moments before the ceremony, said a source.

The ruling 5-Star Movement has blamed Atlantia for the disaster, which killed 43 people.

A large section of the 1.2km motorway viaduct, built in the 1960s with reinforced concrete, collapsed a year ago, sending cars and trucks plummeting about 50 metres to the ground.

5-Star has accused the group of neglecting maintenance on the ageing viaduct and called for its national toll-road concession to be revoked.

Atlantia, controlled by the Benetton family famous for its retail clothing chain, denies the accusations.

It says regular, state-supervised inspections had indicated the viaduct was safe, but the company has struggled to repair its reputation.

This morning, as the head of state, prime minister and other political leaders took their front-row seats for the ceremony, held inside a damaged warehouse at the disaster site, some relatives told Prime Minister Giuseppe Conte they would leave if the Atlantia officials were to stay, the source said.

Approached by Mr Conte's officials, Chief Executive Giovanni Castellucci and Chairman Fabio Cerchiai quietly left the ceremony, the source added.

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The pair are among dozens of company officials under investigation for suspected manslaughter over the collapse. They deny any wrongdoing.

Moments later, the mass, celebrated by Genoa archbishop Angelo Bagnasco, began with the reading out of the names of each of the 43 victims, watched by hundreds of their loved ones.

Rubble and mangled steel still lie strewn across the site.

The bridge's two remaining towers were demolished in a giant blast in June to make way for a new structure.

"This is a day of grief, but also of pride for this city," regional governor Giovanni Toti told reporters as he arrived for the ceremony.

"Grief because we are remembering 43 victims, for whom we hope justice will soon be done ... but also pride because a year on, the city has managed to rise up and is back on its feet."

A new steel and concrete motorway bridge, designed by Italian architect and Genoa native Renzo Piano, is scheduled to be open for traffic in April 2020.