Six people were killed and three are missing after a container ship crashed into a control tower in the northern Italian port of Genoa, rescuers said on Wednesday.

The tower, which was more than 50 meters (160 feet) high and looked much like the ones common at airports, collapsed into the water late on Tuesday after being struck by the prow of the vessel, the Jolly Nero.

Two of the dead were coastguard officers and a third was a pilot for the port, the coastguard said.

The three other victims have yet to be identified. Two were recovered from the wreckage of the tower's lift, a firefighters' spokesman said.

The accident happened as staff were changing shifts and there were 13 people in the tower when it was struck, the coastguard said.

As well as the dead and missing, officials said four people were injured and had been taken to hospital. Two were seriously hurt and one had lost a foot, investigators said.

"The main injuries are fractures, crushed body parts, significant traumas," emergency services doctor Andrea Furgani said.

The crash occurred shortly after 11 p.m. (2100 GMT) in calm conditions as the Jolly Nero was maneuvering out of the port.

Genoa prosecutor Michele Di Lecce has opened an investigation and is focusing on a possible malfunction of the ship's engine or steering mechanism, judicial sources said.

The crash is the most serious maritime accident in Italy since the Costa Concordia luxury cruise liner struck a rock and capsized off the island of Giglio in January 2012, killing 32 people.

"There's no logical explanation because two tug boats were moving the ship and there was a port pilot on board and sea conditions were optimal," the head of the Genoa Port Authority, Luigi Merlo, said.

The only thing left where the tower had stood was a leaning metal-framed stairway. Divers from the fire department joined the search for bodies.

The Jolly Nero, which is 238 meters-long (781 foot) with a gross tonnage of 40,594 metric tons, is owned by local operator Ignazio Messina and Co.

"A thing like this has never happened, we are devastated," said Stefano Messina, one of the directors of the family-owned firm, who was in tears when he spoke to a local TV channel.