The populist government has blamed the operator of the viaduct for Tuesday's collapse that killed at least 38 people in the northern Italian city and threatened to strip the firm of its contracts.
Authorities have planned a state funeral service on Saturday at a hall in Genoa, coinciding with a day of mourning.
Adorned with flowers and photographs, 18 coffins — including a small white one for the youngest eight-year-old victim who died alongside his parents — lined an exhibition centre transformed into a chapel on Saturday morning, according to an AFP reporter.
Firefighters were applauded as they entered the hall ahead of the ceremony, due to begin at 11:30 am.
But more than half of the families of the victims have refused to take part, some preferring a more intimate funeral while others announced a boycott.
According to La Stampa newspaper, the families of 17 victims have refused to take part, while a further seven have yet to decide whether they will attend.
“It is the state who has provoked this; let them not show their faces, the parade of politicians is shameful,” the press cited the mother of one of four young Italians from Naples who died.
Italian President Sergio Mattarella and Prime Minister Giuseppe Conte are due to preside over the state funeral.
The father of another of the dead from Naples took to social media to vent his anger.
“My son will not become a number in the catalogue of deaths caused by Italian failures,” said his grieving father, Roberto. “We do not want a farce of a funeral but a ceremony at home.”
The government has accused infrastructure giant Autostrade per L'Italia of failing to invest in sufficient maintenance and said it would seek to revoke its lucrative contracts.
Interior Minister Matteo Salvini demanded that the company offer up to 500 million euros ($570 million) to help families and local government deal with the aftermath of the disaster.
The service came as firefighters still searching for five missing people discovered a car with human remains inside.
The Civil Protection authorities did not comment on the number of victims but local media reported a family of three were discovered, including a nine-year-old girl, adding to the death toll of 38.
The dead include other children, one as young as eight, and three Chileans and four French nationals.
State of emergency
The Morandi viaduct dates from the 1960s and has been riddled with structural problems for decades, leading to expensive maintenance and severe criticism from engineering experts.
Its collapse prompted fears over ageing infrastructure across the world. Italy has announced a year-long state of emergency in the region. Autostrade, which operates and maintains nearly half of Italy's motorways, estimates it will take five months to rebuild the bridge.
It denies scrimping on motorway maintenance, saying it has invested over one billion euros a year in “safety, maintenance and strengthening of the network” since 2012.
Atlantia, the holding company of Autostrade which is 30 percent owned by iconic fashion brand Benetton, has warned that the government would have to refund the value of the contract, which runs until at least 2038.
Italian Prime Minister Giuseppe Conte said Autostrade “had the duty and obligation to assure the maintenance of this viaduct and the security of all those who travelled on it.”