Silvio Berlusconi, the Italian prime minister, has left a hospital in Milan four days after suffering a violent assault, saying he hoped the attack would usher in a new era of dialogue in Italian politics.

The 73-year-old leader, a small bandage on his nose and a large compress on his left cheek, was seen leaving the institution in a black sedan on Thursday, waving through the rear window to journalists crowded at the hospital gates.

Shortly afterwards, the billionaire issued a statement saying he hoped the attack could teach Italy's political leaders a moral lesson.

"If, after what happened, there is a better awareness of the need for calmer and more honest language in Italian politics, this pain will not have been for naught," he said.

'Climate of hatred'

Berlusconi's assailant, a 42-year-old described by police as having a history of mental problems, hit him in the face with a replica of Milan's iconic cathedral on Sunday.

The prime minister's nose and two of his teeth were broken in the attack which has left both the political left and right accusing each other of creating a "climate of hatred" that provoked the assault.

Berlusconi said his days in hospital left him feeling "loved" by the Italian people.

"I will have two memories from these days [in hospital]: the hatred of few and the love of many, so many Italians," he said.

"Neither the violence of stones nor the worse violence of words ... will prevail. These last days I have felt that even some political opposition leaders have come closer."

Italian media said Berlusconi would head to his villa in nearby Arcore where doctors have advised him to rest for at least two weeks.

A banner reading "Welcome Home" was seen at the entrance to the residence, with security forces keeping journalists a few hundred metres away.

Doctors initially expected Berlusconi's hospitalisation to last 24 to 36 hours, but his stay was extended because of persistent pain and trouble with eating.

Old neck pains that resurfaced after the attack caused Berlusconi severe headaches, but his condition improved overnight Wednesday to Thursday, allowing him to leave the hospital, Alberto Zangrillo, his doctor, said.

Trips cancelled

Massimo Tartaglia, Berlusconi's assailant, could face up to five years in jail if convicted of assault, and remains in custody despite a lawyer request for his transfer to a psychiatric hospital.

The prime minister's nose and two of his teeth were broken in the attack [AFP]

The head of a vast media empire, Berlusconi has targeted prosecutors seeking his conviction on corruption charges, as well the country's constitutional court, which threw out an immunity law that protected him from prosecution while in office.

Last month, after a Mafia turncoat alleged he had links with organised crime in the early 1990s, Berlusconi threatened to "strangle the authors of fiction about the Mafia".

Berlusconi, now in his third term as prime minister, is also fighting mounting domestic troubles. Allegations about dalliances with other women led his wife Veronica Lario to file for divorce.

Acting on doctor's orders, the prime minister called off a trip to the Copenhagen climate summit this week and a Christmas Eve trip to L'Aquila, the Italian city where nearly 300 people died in an earthquake in April. 

In a second security scare, a 26-year-old man was arrested in the early hours of Wednesday while seeking to reach Berlusconi's hospital room.

The intruder, who police said has also been treated for mental health problems, was arrested coming out of the elevator on Berlusconi's ward where he explained he wanted to "talk" to the prime minister.