A health board has declared a major incident and has asked patients to only attend one of its hospitals in life-threatening cases.
Aneurin Bevan University Health Board in Wales has said its services are under "under sustained and unprecedented pressure".
The health board has declared a "business continuity incident" - known as a black alert - which is the highest alert level available.
A spokesperson told Wales Online the Grange University Hospital in Cwmbran is seeing "a record number of attendances" and that non-life-threatening patients were waiting more than 14 hours to see a doctor.
Saying it had "very few beds available" across its hospitals, a health board statement asked patients only to attend the Grange if their condition was life-threatening or if they had a serious injury.
The health board's statement on Tuesday evening read: "The health board is under sustained and unprecedented pressure. Despite actions to try to stabilise our services today we have had to declare a state of ‘business continuity’.
"Our emergency department at the Grange University Hospital is extremely busy, and we have seen a record number of attendances, and waits to see a doctor, in some cases, are greater than 14 hours where the patient’s condition isn’t life threatening. We have very few beds available across our hospitals to accommodate patients requiring admission.
"We need to ask for your support and to only attend the Grange University Hospital if it is life threatening or you have a serious injury."
It added that these cases would include "severe breathing difficulties, severe pain or bleeding, chest pain or a suspected stroke, or serious trauma injuries, such as from a car crash.
"If you have a less serious injury then please visit one of our Minor Injury Units in Newport, Abergavenny or Ystrad Mynach," it added.
"If you need medical help, please think carefully about the services you choose."
An urgent message from the health board reads: "If you have a loved one in hospital who is deemed medically fit to be discharged, please consider taking them home and caring for them.
"If your loved one is medically fit to be discharged, then hospital is not the best place for them to be – they will recover better at home. If your loved one is medically fit for discharge, our staff will contact you to discuss the next steps.
"We are asking families to help in this way because it is best for their loved one and will free up hospital beds for sick patients who need to be admitted to hospital."
