All telephones and IT systems are currently down at Peterborough City Hospital.
The hospital in Bretton is experiencing a “major communications failure,” it said.
Visitors are being asked not to attend “unless absolutely necessary”.
The hospital said that patients are not affected with the building retaining power.
Engineers have been called to the hospital.
In a statement, the hospital said: “We are currently experiencing a major communications failure at PCH.
“All of our telephones and computer IT systems are down and we are unable to take calls both internally and externally.
“We are asking patients to be mindful before coming to the emergency department and ask that you attend for urgent treatment only.
“If you require maternity advice over the phone then you can call the Hinchingbrooke maternity unit on 01480 847480. If you are in labour or think you need to attend the PCH maternity unit urgently, they remain open to new admissions so please attend as usual.
“Given the increased activity, we are asking visitors not to come in unless absolutely necessary. Please be assured our patients are not affected by this issue - we still have power to the building, this is a communications failure only.
“A hospital control team are meeting to discuss a plan of action and engineers have been called to look at the fault. We will update you on the situation later today.”
Updates will be given at: https://www.facebook.com/PboroCityHosp/.