WINNIPEG -- Manitoba's largest hospital is placing restrictions on after-hours visitors in an attempt to improve security.

Winnipeg's Health Sciences Centre says starting Wednesday on a trial basis, exterior doors and in-patient care units will be locked at 8:30 p.m.

Visits to the palliative and end-of-life units, as well as to patients facing critical changes to their condition, will be limited to designated family members.

The current practice of security staff screening anyone requesting access after hours will continue, but visitors will be screened again at the in-patient care unit.

Around-the-clock access to the adult and children's emergency departments will continue.

The new measures will be evaluated by hospital staff at the end of November.

The changes follow a number of incidents at the Health Sciences Centre involving aggressive patients -- some high on crystal meth -- who have attacked medical staff and security officers.

The hospital recently increased security in its adult emergency department, parkades and the area around the complex.

"This is an issue that's been impacting staff and patients who are generally trying to rest and stay safe at night," said Ronan Segrave, HSC's interim chief operating officer.

"Through consultation with staff, we have recognized and understood this to be an important issue."