He also said he would make an initial €5m ($5.7m) available from central funds to the north-western region.
The regional government had requested the action following Tuesday's disaster, which left 39 people dead.
There has been anger and disbelief in Italy that such a vital structure could have simply given way.
Rescuers have said there is little hope of finding more survivors underneath the Morandi bridge, where dozens of vehicles fell from a height of 45m (148ft) in Tuesday morning's collapse.