The injured nurses were treated at the hospital and have been able to go home, according to the NSW Nurses and Midwives Association.
General secretary of the nurses union, the NSWNMA, Brett Holmes, has called for a full investigation into the violent incident, which he described as disturbing.
“This is a terrible situation where three nursing staff have been injured during the course of their work, let alone the other elderly patient who has also suffered injuries,” Mr Holmes said.
“It’s unfortunate that violent incidents of this nature continue to occur in our hospital settings.”
The alleged attacker was receiving treatment under police guard in hospital on Sunday morning as inquiries continued.
Sydney Local Health District has been contacted for comment.
NSW Premier Gladys Berejiklian said she was relieved to hear the victims were recovering.
“I was really concerned to hear about those early reports,” Ms Berejiklian told reporters.
Ms Berejiklian said her Health Minister Brad Hazzard has recently launched a major investigation into the security at hospitals.
“Of course the government will adopt any further recommendations we need to,” Ms Berejiklian said