At least seven people have been killed and more are missing after the cargo ship Jolly Nero slammed into a control tower at the busy port of Genoa late Tuesday night.
Three people appear to have been trapped in an elevator in the tower that fell into the water, according to the BBC.
The accident took place during a shift change when at least 14 people were inside the concrete structure. Only one victim, a 30-year-old coast guard, has yet been identifed.
Rescue workers are probing through the rubble of the control tower, where it's believed many of the victims have been trapped.
Port officials were mystified over how the 40,500-ton, 655-foot Jolly Nero managed to smash into the tower, which was used by harbor pilots to control the entry and departure of vessels from Genoa.
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"It's really difficult to explain what happened, because the ship was not supposed to be there," Luigi Merlo, president of the Genoa Port Authority of Genoa, was quoted telling Italian media. "What has happened is really inexplicable."
Italian news reports that a motor failure may have caused the cargo ship to veer off course and crash into the 165-foot concrete and glass high tower at the harbor entrance.
Whatever the cause, the incident is sure to raise questions about safety in Italian waters following last year's Costa Concordia disaster which cost the lives of 32 passengers and crew when the cruise liner ran aground off the island of Giglio.
Italian prosecutors want the Costa Concordia's captain Francesco Schettino to stand trial for manslaughter, causing a shipwreck and abandoning the ship before all the 4,200 passengers and crew were evacuated.
In Genoa, the Jolly Nero has been confiscated from its owner, the Ignazio Messina & C shipping company, which owns 14 other cargo ships.
Prosecutors opened a manslaughter investigation into "persons unknown."
Paul Ames contributed to this report from Brussels, Belgium.