Six people were killed Friday when the Italian port city of Genoa was hit by flash floods during heavy rainfall, including a woman who was apparently crushed by cars being swept away by the water.

"There have been six deaths," said the local prefect, Francesco Musolino.

Hundreds of shops were flooded and emergency officials urged residents to move to high ground and upper floors as waters rose and firefighters used rubber dinghies and divers to evacuate people, officials said.

Five of the victims, including two children, died when the lobby of an apartment block in which they had sought shelter flooded.

"This was a completely unexpected tragedy," said Genoa mayor Marta Vicenzi.

Motorways in the area were also closed off and flights re-routed away from the local airport. Schools will be shut on Saturday.

"People should avoid bridges and streams and not sleep on first floors or in areas that are easily flooded," said Renata Briano, a local emergency official.

Briano said residents of the northwestern city should "stay safe and head for high ground if in danger" as well as avoid using cars unless absolutely necessary.

The head of the local Liguria region, Claudio Burlando, warned that the situation was "critical," adding: "Moving around is really dangerous."

The flooding comes after heavy rains last week killed 10 people and caused tens of millions of euros (dollars) in damage in Liguria.