Eight people were injured on Saturday when a car drove into pedestrians in the centre of the northern Italian city of Modena, police and the city's mayor said.
Police said they arrested the driver, a man in his thirties, and there was no further danger.
Modena's prosecutors said in a statement on Sunday that the suspect is under investigation for massacre and personal injury, adding that efforts are under way to establish the motive behind his actions.
Among the injured, four people are in a serious condition, two had suffered the loss of their legs, with one in a life-threatening condition, the prosecutors added.
The driver is an Italian national born in Bergamo, of North African origin, and a resident of the Modena area, the mayor added.
"It seems (the driver) deliberately drove onto the sidewalk, hitting several people and crashing into a shop window. He then got out of his car and brandished a knife," said Mezzetti.
"The man had received treatment for mental health issues in 2022 due to schizoid personality disorder, after which he went off the radar."
One man who tried to stop the driver suffered minor injuries, the mayor said.
A witness told RaiNews24 he heard people falling and threw himself to the ground as the car approached. He said the driver appeared to be under the influence of alcohol or drugs, though authorities have not confirmed this.
Prime Minister Giorgia Meloni travelled to Modena on Sunday, cancelling a meeting in Nicosia with Cyprus' president in order to make the trip, government sources said.
Italy's President Sergio Mattarella will also travel to the Italian northern city, the sources added.
"I express my solidarity with those who were injured and their families," Prime Minister Meloni posted on social media X
"What happened in Modena is extremely serious," Meloni added.

India detains thousands, locks down Delhi to foil election chief protest
Isaias kills 2, leaves thousands without power after landfall
Russian attack on Ukrainian city kills 12
Abbas postpones Palestinian elections, sets poll for September 2027
Magnitude 7.7 quake shakes Panama, canal operations normal
US imposes sanctions on International Criminal Court
Three Saudi nationals killed in attacks on Riyadh airport, aviation authority says
Former ICC judge Navi Pillay wins 2026 Nobel Peace Prize
