NHS procedures and appointments across north Wales have been cancelled after a health board delcared a "critical incident" caused by unprecedented demand.
Betsi Cadwaladr University Health Board (BCUHB) say they have postponed "all but the most urgent procedures and appointments" due for Tuesday 3rd January.
All affected patients will be contacted directly by the health board.
Wales' Chief Medical Officer Frank Atherton said Wales' hospitals were under unprecedented pressure before the new year as health boards across the country urged people to avoid emergency departments unless they were experiencing life threatening illness.
The NHS 111 Wales helpline has also experienced unprecedented demand, with a record number of calls received in one day on Tuesday 27th December.
The Welsh Ambulance Service, which runs the helpline, advised people they could be on hold for several hours before their call is answered.
BCUHB is Wales' biggest health board and runs three major hospitals - Ysbyty Glan Clwyd, Ysbyty Gwynedd and Wrexham Maelor Hospital.
"This morning we have declared an internal critical incident as we are struggling to cope with prolonged, unprecedented demand across the health and social care system," said Angela Wood, Executive Director of Nursing and Midwifery at BCUHB.
"We are currently seeing a very high volume of patients presenting at our hospitals with flu, COVID and other respiratory viruses, as well as in increase in the most seriously injured or unwell patients requiring emergency care.
"This, together with a lack of available beds in our hospitals and significant staffing shortages, is leading to extremely long waits for patients to be seen – particularly at our hospital Emergency Departments.
"Similar pressures are being experienced in other Health Boards and English Trusts."
She continued: "We are continuing to work closely with Local Authority colleagues to support medically fit patients to be discharged from hospital and we are making use of all available staffing.
"This is an exceptionally challenging time for colleagues across our health services and we are hugely grateful for the continued efforts being made in such difficult circumstances."
People are being advised to use the NHS 111 Wales website which will help them determine whether they need self-care at home, a visit to a pharmacy, an appointment with a GP, a trip to a minor injuries unit, or a hospital emergency department.
Swansea Bay NHS Trust put out a warning to people not to attend Morrison Hospital's A&E department unless their condition is life-threatening, due to long waits, and advised people to use the minor injuries unit at Neath Port Talbot Hospital.