The public have been warned they will face a lengthy wait at Altnagelvin Hospital's A&E if their condition is not life-threatening.
It comes as it emerged that one sick person waited for four days in the Derry hospital for a bed.
On Monday, the Western Trust said that its emergency department is under "extreme pressure" with 84 patients in the department, 34 waiting to be admitted.
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The hospital is warning of lengthy waits for those who do not have life-threatening injuries and has signposted patients to other services.
Emergency Medical Consultant, Dr Sandy Nelson, said the A&E department at the hospital was currently "under extraordinary pressure".
He added: “At the moment I’ve got 84 patients in the Emergency Department, 34 of them are awaiting a bed and one of those patients has been waiting four days for an in-patient bed.
“I’ve got patients that are sitting in corridors in chairs for 24 hours before we can physically put them in a bed to lie down,” he added.
“In these circumstances we are all under extreme pressure and there’s a few things you can do to help us.
“Please do only attend if it is an emergency and you have no other option.
“We will see patients with true medical emergencies and psychological emergencies as soon as we can.
“But if you can help us by only attending by yourself and being patient with our staff and giving them the respect they deserve that would be extremely helpful.”
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