The Royal Cornwall Hospital has gone into its highest state of alert because of high demand on its services.
It's the first time this year the hospital has gone onto black alert, which means there aren't enough beds to cope with admissions.
At this stage it just applies to the hospital trust, not the wider health care system in Cornwall.
In response to this the Royal Cornwall Hospital Trust has implemented its 'significant internal incident plan'.
The alert means extra staff may be brought in, and some non urgent operations could be cancelled.
A hospital spokesperson told ITV News it is difficult to know how long the black alert will be in place, but it's reviewing the situation every few hours.
THINK BEFORE VISITING A&E
In the meantime the RCHT is urging patients who don't need emergency care to use other services like GP's and pharmacies to help ease the pressure.
- More: what service do I need?
WHAT DOES BLACK ALERT MEAN?
This is the highest level of alert, which usually means bed capacity has been reached and that patients arriving at A&E will have to be taken to another hospital. Sometimes routine operations will be cancelled to free up bed space.
NHS England classifies a black alert as a "serious incident". It means the system is under severe pressure and is unable to deliver certain actions and comprehensive emergency care.
It also means there is potential for emergency care and safety to be compromised. Decisive action must be taken to restore the hospital's capacity and ensure patient safety.