Christchurch Police are defending their decision for not going to a serious incident at Hillmorton Hospital.
Police were called there just after nine o'clock on Saturday night when a patient allegedly attacked nurses.
Senior Sergeant Vaughn Lapslie said within three minutes of the attack taking place they were told the alleged offender was restrained and were sent to another mental health issue in Christchurch.
Police did not return to the hospital again until 10:40pm.
They have confirmed that three nurses were involved in the incident.
The Press reported the alleged offender attacked three nurses, biting one's finger to the bone, severely beating the second and hitting the third in the jaw. All three were taken to the Christchurch hospital emergency department.
They also said the alleged attacker was in a methamphetamine psychosis when the attack took place.
In light of the incident on Saturday some student nurses have become nervous entering the mental health industry, especially without training of self defence when studying.
One student nurse said she "would think seriously before entering the mental health industry."
Another said she wants to be able to rely on Police when working with mental health patients.
Police said they diverted the unit on the way to the hospital when a more urgent incident came up.
Acting district Commander Inspector Tony Hill said "within three minutes of receiving the request, information was relayed to police the alleged offender had been restrained and placed in a secure room."
He also said the three staff members involved and attacked have received medical treatment for their injures.
Police said an investigation is underway into the alleged assault.
Canterbury District Health Board general manager mental health services, Toni Gutschlag, said staff were doing an excellent job and will continue to support them.
Hillmorton Hospital did not want to comment on the incident as the investigation is on-going.