Patients are being told to use the emergency department at Nottingham's Queen's Medical Centre only in a "real emergency" after a rise in admissions.
Nottingham University Hospitals NHS Trust said there had been a significant increase in patients since the weekend.
A spokeswoman said the average daily attendance in February rose to 454 from 424 in 2007 - up by 7%.
People are being asked to consider seeing their GP or contact NHS direct being going to the hospital.
The hospital spokeswoman said winter was a traditionally busy time for hospital staff because of colds and flu viruses and respiratory diseases.