Shares in the operator of the section of motorway that collapsed in Genoa slumped as much as 24%, wiping more than €4.6bn (£4.1bn) off its value.
The exact price of Atlantia stock was difficult to calculate as it was so volatile in opening Milan trading that traders were not able to get a fixed price.
Under stock market rules, trading is suspended if the shares rise or fall by more than 10% in value.
Toll-road group Atlantia has come in for sustained criticism from politicians, following the disaster on Tuesday.
At least 39 people died when an 80-metre stretch of bridge crashed to the ground and its feared up to 20 people may be buried under the rubble.
Autostrade per l’Italia, part of Atlantia and owned by Italy’s Benetton family, operates the A10 motorway that includes the bridge. It is responsible for about 3,000km of Italy’s motorway network.
The company said world-leading experts made regular safety inspections of the 1.2km-long bridge and it completed an overhaul two years ago.
Atlantia said the maintenance work was “approved by the transport ministry in accordance with the law and the terms of the concession agreement”.
But Italy’s populist government has attacked the Benetton family and the European Union over the collapse.
Italy’s Prime Minister Giuseppe Conte said he intends to revoke Atlantia’s concession to operate the motorway.
The government also intends to fine the firm €150m (£134m).
Luigi Di Maio, leader of the Five Star Movement and Italy’s deputy prime minister, claimed motorway tolls could be nationalised as he took aim at big business.
“It’s not possible that someone pays a toll to die,” he said.
“Those who were supposed to do the maintenance work did not do it properly. That bridge should have been closed before this tragedy happened.
“The profits that these companies make as monopolies anger many people … a lot of money should have been invested in security, but instead it went towards dividends.”
Atlantia had revenue of €5.97bn in 2017. It made a profit of €1.4bn and paid out €1.17bn to shareholders, according to the company’s accounts.
Mr Di Maio also attacked the Benetton group, the family-run firm which controls Autostrade through a holding company as well as many other assets.
He accused previous governments of turning a blind eye to the state of the country’s motorways because of their desire for political contributions.
Atlantia said the decision to revoke its licence had been taken unilaterally and said compensation would be due if toll contracts were ended early.
“The announcement was publicly communicated lacking a specific default notice and without any verification of the material causes of the accident,” the firm said in a statement.
The company is expected to hold an extraordinary board meeting next week.
Matteo Salvini, the leader of the Northern League, which is in coalition with Five Star, condemned European Union budget constraints in the wake of the disaster.
“We should ask ourselves whether respecting these limits is more important than the safety of Italian citizens. Obviously for me, it is not,” he said.
From – SkyNews