Patients at Royal Liverpool University Hospital's accident and emergency unit are facing waits of up to 50 hours.
Liverpool University Hospitals NHS Foundation Trust has declared a "critical incident" due to "exceptionally high demand" on services and urged people to only go to A&E in a genuine medical emergency.
The hospital said it was "extremely busy" amid a rising number of patients with flu and other respiratory conditions, prompting Liverpool Riverside Labour MP Kim Johnson to call on the government to immediately come up with a plan to increase NHS funding.
Critical incidents have also been declared in the East Midlands, Devon and Cornwall.
