An outbreak of diarrhoea and vomiting has been cited as one of caused of the 'critical incident' alert raised by Royal Cornwall Hospital on Monday.
In a letter to MPs, Health Secretary Matt Hancock said the outbreak, which began in care homes, caused a "significant number of bed closures".
The hospital has since managed to "step-down" from the highest alert level.
Theresa May has said the Government 'is aware' of the issues currently faced by Royal Cornwall Hospital, after it declared a 'critical incident'.
A queue of fifteen ambulances were waiting outside A&E to admit patients on Monday night.
A number of appointments have been cancelled, and patients are still being urged to seek alternatives before visiting the hospital or dialling 999.
MP for Truro and Falmouth, Sarah Newton, raised the issue in Prime Minister's Questions on Wednesday [10 July].
She said the situation RCH found itself in was "extremely worrying for all families across Cornwall who rely on" the hospital and its services.
The highest operation pressure level - known as OPEL 4 - was declared on Monday (July 8) after patients were reportedly treated in hospital corridors and up to 15 ambulances were left waiting.
A spokesperson for Royal Cornwall Hospital Treliske (RCHT) said the trust was liaising with Cornwall Council and other agencies as they work together to deal with the situation.
Due to extreme pressure on services across Cornwall, leaders of the health and care services have declared a major incident.
Advice for patients
A number of routine outpatient appointments have been cancelled at the Royal Cornwall Hospital in the wake of the major incident being declared.
Staff say patients are being contacted personally, and so do not need to call the hospital.
Urgent cancer clinics and renal dialysis are not affected by the incident.
A spokesperson said any cancelled appointments will be rescheduled as soon as possible.
We do apologise for any inconvenience but hope patients will understand our need to concentrate on caring for the high number of emergency patients needing admission.