At least seven people have died and several are missing in the water at the port of Genoa, after a container ship, the Jolly Nero, hit a control tower in a night-time accident.
The collision on Wednesday, which saw the vast metal structure bend by 45 degrees, revived painful memories in Italy of a deadly cruise ship disaster last year.
Part of the tower, in which about 14 people were present at the time of the accident at around half past midnight local time, crashed into the water.
One of the victims was reported by some media to be a woman in her 30s, while the other two were male.
Rescue workers dived into the waters around the port - one of the busiest in Italy - in a frantic search to find about 10 people believed to be missing. Six others were reported seriously injured.
An employee of the Messina Line company, which is based in Genoa and owns the Jolly Nero, confirmed that "there was an accident when the ship was leaving the port. It ran into the tower, but we don't know why at this point, nor how many people are hurt".
Emergency services at the scene in Genoa said it was not clear whether some of those still missing were trapped within the lift inside the tower.
Rescuers were using dogs trained to find people in earthquake zones to see if survivors were trapped under the rubble around the tower.
Genoa mayor Marco Doria said Italians were in mourning after this "very serious port accident which struck an entire city".
The Italian container ship is almost 200 metres long, 30 metres wide, and has a gross tonnage of more than 40,500. It was bound for Naples.
"We are desperate"
Stefano Messina, the ship's owner who arrived at the port soon after the crash, choked back tears as he told journalists: "We are all utterly shocked. Nothing like this has ever happened before, we are desperate."
Prosecutors in the northwest city opened an investigation while the Jolly Nero was sequestered by police, and the captain detained for questioning, reports said.
"I heard a terrible din and rushed out of my cabin," Roberto, the port's night watch, told the La Repubblica newspaper. "It was an incredible sight: the control tower was leaning perilously."
The impact happened during a shift change at the tower which meant that more people were present.
Three people were believed to have been trapped in the lift of the control tower and may have fallen into the sea.