A delusional patient at a secure unit in Melbourne ambushed a nurse and bashed him with a motorcycle battery, sources have told Fairfax Media.
They say the nurse was lucky not to have been killed by the patient, who had been due to be discharged.
It was the second of two violent attacks by different patients against nurses at Austin Health's Secure Extended Care Unit in Heidelberg within just three days last month.
The incidents are now subject to an internal review.
Although the facility cares for many difficult and longer-term psychiatric patients, the incidents have rattled staff, who say system and staffing pressures meant warning signs were not acted on.
Police have laid charges after the first incident on October 16, which involved a known dangerous inpatient who had reportedly previously been involved in an assault at Dandenong Hospital that left a nurse with bleeding on her brain.
It is understood that the man was considered so unwell and aggressive that he was watched by a security guard and nurse around the clock but managed to assault a senior staff member, allegedly punching him in the head multiple times.
"He is very big and he hurts people," one nurse said.
Although sources said the patient was mentally unwell at the time, he has been charged over the incident and is in custody.
The attack involving the motorcycle battery happened two days later.
Staff at the secure unit said they were particularly disturbed by the second incident, because the patient involved was well liked and was about to be discharged.
They said the man seemingly lay in wait in the lobby area of the unit on October 18, armed with a motorcycle battery in a bag, and then launched an attack on a male nurse returning from a break.
Sources said the nurse could have been killed, if another male nurse who was able to restrain the patient had not been close by.
"He would have killed him, no doubt," said a staff member, who was working on the day of the assault.
"There was significant amount of blood coming from the nurse's head.
"He's not a big guy that got attacked. He was so lucky where he got hit. He just went white. He had no idea what happened."
The victim suffered a gash to the back of the head, it's understood.
An Austin Health spokesman said it was conducting an internal review of the incidents "as is normal practice" and the attacks had been reported to police.
"Both nurses received immediate clinical care and counselling and are back at work," a spokesman said.
"Counselling has also been arranged for all staff involved including incident debriefing sessions."
The spokesman said extra cameras had been installed among other new security measures at the unit.
"We know that hospitals and mental health treatment facilities can be highly challenging environments. But the safety of our patients and staff is our highest priority," he said.
"Austin Health has a robust system in place for escalation of clinical concerns for all psychiatric patients."
However, a nurse said the second attack could have been avoided, as staff knew the man had become increasingly unwell and delusional.
The nurse said they first requested a doctor see him on Saturday, but a review from a psychiatrist did not take place until Monday.
They said the nurse who was attacked was unaware that the patient had become paranoid about him.
"All the focus went on the first attack, so this guy went under the radar," the nurse said.
"But all the symptoms and alarm bells were there on Saturday.
"I don't think the staffing levels are adequate for the unit anymore, for what we are having to deal with."
The Austin spokesman denied that a shortage of staff had been a contributing factor.
"At the time of both incidents we had full staffing plus additional, around-the-clock, one-to-one nursing and security staff.
"Psychiatry reviews took place in the days prior to this incident."
A health department spokeswoman said it was "confident in Austin Health's processes and handling of the matter".
Health and Community Services Union state secretary Paul Healey said there was a state-wide shortage of staff and violent incidents were "driving qualified, caring people out of our mental health system and causing them to have their own mental health issues".
Victorian Mental Health Minister Martin Foley said "after any incident takes place in our hospitals the health service notifies the relevant authorities, such as WorkSafe Victoria or Victoria Police".
He said the Victorian government had spent $40 million on a package of anti-violence measures for hospitals, including a Safewards program targeting 18 mental health services.