Due to 'increased pressure on its emergency department.'
Derriford hospital in Plymouth has decalred a critical incident due to a "significant and rising demand for hospital care".
The hospital says the number of people attending the Emergency Department and other emergency facilities who need treatment is much higher than normal.
Over 300 people attended Derriford Hospital as emergencies on Monday and nearly 200 of those needed admitting for care as inpatients.
The University Hospitals Plymouth NHS trust says they are particularly seeing high numbers of older patients with respiratory problems caused by the cold weather.
The number of people in England's hospital with flu quadrupled in the last month, according to NHS data.
Darryn Allcorn, Chief Nurse at University Hospitals Plymouth NHS Trust, said: “Our Emergency Department is there for life-threatening conditions and real emergencies. If you can use other services, such as NHS 111, pharmacy or your GP, please do so. If you do come to the Emergency Department and it is not an emergency or a life-threatening condition, then you may be redirected.
“It’s really important we make sure that the sickest patients are prioritised and that we keep our services flowing for those who are in greatest need. Therefore, we ask that at this time unless you are a carer or if the patient who is coming to the hospital is particularly distressed, that those who accompany patients do not to come into the Emergency Department. We need the seating spaces for patients to sit down and be comfortable.
“We ask that patients, visitors and families be kind to one another and continue to treat staff with respect during this extremely busy period.”