Hinchingbrooke Hospital has warned it is having "serious issues'" with demand for its accident and emergency department.
The hospital, in Huntingdon, Cambridgeshire, is asking people not to go A&E unless they have life-threatening symptoms.
Bosses say acute admissions have rocketed, and are much higher than would be expected for this time of year.
They say overcrowding has been made worse by staff sickness and a slower discharge time for patients.
Anyone with a non-life threatening condition are advised to visit their GP or pharmacy instead.