The Welsh Ambulance Service is urging people to be honest about the nature of their illness when calling the emergency services for help.
It said it has become "apparent" that some members of the public have been "withholding information" about their illness during the coronavirus outbreak because they are worried an ambulance will not be sent.
It means paramedics have been attending some incidents without the right protective equipment, exposing crews to "potential harm" the service added.
Lee Brooks, the Trust's Director of Operations said staff are working "tirelessly" to provide the best possible care.
“This is unchartered territory for our generation, but our plans continue to develop as we work with our partners to ensure that we deliver care as safely and effectively as possible."
The service is asking the public to be open and transparent about the nature of their call and their symptoms.
Mr Brooks added, “Some of you have told us that you were concerned that, had you been honest, an ambulance would not have been sent.
“We understand your concerns but I want to make a couple of things clear. Firstly, we will always send an ambulance where it is warranted, but this means relying on what our call handlers are told at the point that you call us.
“If you don’t give us accurate information, you risk the welfare of the people whose job it is to care for us all. This is incredibly unfair on our staff, as it means that their right to enter your home prepared has been removed.
“Personal protective equipment is worn by our staff to protect them from contracting the disease.
“I must ask everyone who calls either 111 or 999 to be honest with us about what’s wrong with you and allow us to signpost you to the right care.
“These are difficult times for us all, but please don’t put our staff in harm’s way when they just don’t need to be.”
Lee added: “Please heed the official advice from government and Stay At Home, Protect the NHS, Save Lives.”
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