Patients have been warned not to visit Southend University Hospital unless seriously unwell or critically ill.
The hospital has become the latest in Essex to declare a 'black alert' due to a higher than usual number of acutely ill patients requiring a hospital bed.
Choking, chest pain, blacking out, blood loss and fractures are all considered emergencies.
It follows Colchester and broomfield in advising patients not to visit unless completely necessary.
Sue Hardy, acting chief executive at Southend University Hospital, said: "The health system in Essex is under significant pressure today with lots of illness in the community.
The emergency department is extremely busy and patients are being warned that those attending with 'non-urgent' conditions will wait much longer than usual as patients are prioritised according to how unwell they are.
"We would like to remind anyone who is unsure of the best course of action to always ring NHS 111 for health advice 24 hours a day, seven days a week."
Patients have also been advised to visit St Luke's Walk in Centre, Pantile Avenue, Southend which is open at weekends and Bank Holidays from 8am to 8pm.
The walk-in service offers treatment, information and advice for a range of minor illnesses and injuries including.
Dr Roger Gardiner, lead clinician for NHS 111 and out of hours services in south Essex, said: "NHS 111 is available around the clock if you need urgent medical help that is not an emergency.
You will speak to highly trained call handlers, supported by experienced nurses or paramedics who will clinically assess you, provide appropriate advice or refer you to the most appropriate NHS service."
You can also contact NHS 111 for an appointment with your GP's out-of-hours service which runs from 6.30pm until 8.00am Monday to Friday and all day at weekends and Bank Holidays.
