A psychiatrist has died after being stabbed 40 times by one of her patients during an appointment at a public health facility in Italy, investigators said.

Police said the attacker, a man in his 40s with a history of drug and alcohol abuse and a criminal record for drug dealing, was subdued by a colleague of the 53-year-old doctor after the attack during a private meeting in Bari, a city in the southern region of Puglia.

Prosecutors said investigators were examining the attacker's medical records to find out why he was undergoing treatment. No motive for the attack was immediately known.

Puglia's health commissioner, Elena Gentile, said she was told that the attacker had sat calmly in the waiting room for 30 minutes before his appointment, showing no signs of agitation.