The E tū union is calling for district health boards to stop using security contractors after a security guard was viciously assaulted at Waikato Hospital early on Wednesday morning.

Photo: Supplied / Waikato DHB / Facebook

The woman suffered multiple injuries to her head, face and body and remains in the hospital's high dependency unit.

Four nursing staff also suffered minor injuries.

E tū Waikato senior organiser Iriaka Rauhihi visited her in hospital.

"I was actually in tears when I saw her. Just the feeling of seeing someone looking lifeless in a bed," she said.

"I understand she's got a potentially fractured jawbone, eye socket and she's got several stitches throughout her head."

Ms Rauhihi said the assault was believed to have involved a hospital oxygen tank or fire extinguisher, although she couldn't confirm that.

The union said it had multiple issues with the hospital's security contractor, Allied Security, and it wanted DHBs to stop outsourcing the protection of patients and staff.

"The DHB have an absolute responsibility - they're the PCBU [Person Conducting a Business or Undertaking], they're the ones who engage contractors and in this case it's Allied Security.

"Our preference is to have all workers directly employed rather than looking at contractors. While we are dealing with some contractors, not all of them are the same. We have a relatively positive relationship engagement with most contractors. This particular one, we do not."

She said security staff were working far more hours than they should, adding to the risks involved with an already risky job.

"Guards are feeling very tired and overworked. Some are having to work extraordinary hours ... they're heavily short-staffed in some cases."

A 35-year-old man has appeared in court over the Waikato Hospital incident, facing multiple charges including causing grievous bodily harm, assault and wilful damage.

A Waikato DHB statement said the incident was "very" concerning and an investigation was being carried out to see whether anything could have been done differently.

"Waikato DHB is very conscious of providing a safe environment for its staff and contractors, no one should have to face this kind of physical attack at work and we are very concerned that this happened in our hospital."

It said Worksafe has been contacted and the guard and her family are being offered support.

Allied Security did not respond to requests for comment.