A security guard was seriously injured and four nursing staff assaulted at Waikato Hospital this morning.

Waikato DHB executive director of public affairs, Lydia Aydon, said there was an incident on one of the Waikato Hospital surgical wards at around 2am.

"Four nursing staff and a security guard were physically assaulted by a patient who was receiving treatment in the hospital," Aydon said.

"Hospital security and police attended and the patient was arrested.

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"Three staff members received minor injuries and the security guard had more serious injuries.

"All were treated in the hospital's Emergency Department, three were discharged and the guard has been admitted to the hospital."

The female guard was reported to be in the high dependency unit.

It was believed the patient used an oxygen cylinder to assault the staff.

The security guard was being hailed a hero for stepping in to stop the assault, a source told Stuff.

Aydon said all staff involved had been offered workplace support.

The DHB and Worksafe are investigating the incident.

A Police spokesperson said a 35-year-old man is due in court in Hamilton tomorrow.

He is charged with three counts of assault with intent to injure, wounding with intent to injure, injuring with intent to injure, and wilful damage.