Melbourne parents and carers have been asked to think twice about whether their children need to visit the emergency room, as the city's major children's hospital grapples with extreme demand.

The Royal Children's Hospital was on Saturday diverting some patients away from the facility if they required less urgent care than others.

The hospital and its emergency department were experiencing extremely high demand and extended wait times, which were expected to continue during the weekend.

"The most seriously injured or sickest children will always be seen first. Therefore, we are currently working closely with The Department of Health an Ambulance Victoria to divert less urgent care where possible," the hospital said on social media.

"During this time, we ask our community to consider your child's health needs carefully."

Families are urged to contact their general practitioners, their local pharmacists, or Victoria's Nurse on Call service if possible.

The hospital remained open for all urgent medical emergencies and trauma care, and said those with children in need of immediate medical attention should contact triple zero.

It is the second time in seven days the hospital has warned it is under extreme pressure. Last Sunday, it told parents and carers they should visit their local hospital's emergency department instead if possible.

They also asked that only one parent or carer accompany a child to the emergency department where they could.