It is extremely concerning there's now been four assaults this year on hospital security guards working for the same company, a union says.

Photo: RNZ / Karen Brown

E Tū union said the fourth assault involved an Allied Security guard being attacked in the Emergency Department at Christchurch Hospital on Queen's Birthday.

It comes just weeks after an earlier serious attack on another guard at Waikato Hospital left her with a broken arm and multiple facial fractures.

Another two guards remain off work after serious assaults at Hillmorton Hospital and another at Christchurch Hospital.

Mat Danaher from E Tū said there had been growing violence against hospital staff recently and safety had never been more important.

"It's got to be managed properly ... so that the staff, the patients and the visitors are feeling safe," he said.

"If there's one place that people should feel safe, it's a hospital."

Mr Danaher said the union had raised safety issues with Allied Security before.

"We've lost any confidence they're up to the job," he said.

He's advocating for security guards to be employed in-house instead of being contracted through companies like Allied Security.

Allied Security declined to comment.

A spokesperson told RNZ that the managing director was currently on annual leave and would be away for a number of months.