The Royal Cornwall Hospital is urging people to use alternative services as it admits it is under "considerable pressure".
The plea comes just three days after the Emergency Department in Truro announced it would be re-directing all minor injuries to other services during the New Year period.
A spokesperson for the hospital said it was due to the "significant pressure" the service is under.
The trust which runs the hospital said: "We really do need our local population to use alternative services including self care (particularly for colds, flu-like symptoms and diarrhoea and sickness), pharmacies, GPs, minor injury units and calling 111, so that our hospital staff can concentrate on those who really need their specialist care."
We need the help of local people and holidaymakers in choosing well so that we can safely care for those in genuine need of urgent, life-saving care. Please can you support with the usual information.
Anyone who arrives at Truro's Emergency Department with minor injuries or ailments will not be seen and will be redirected to other services.
The NHS Trust has stressed that people should go directly to these services to save any extra time or resources being used. They said: "It will help us significantly if people go to those other services first."