Staff at an A&E department have apologised for "struggling to provide the care patients deserve", adding some were waiting two days for a bed.
The team at Ysbyty Gwynedd in Bangor tweeted to say they were "hamstrung" by the emergency department being full of patients waiting for medical beds.
Betsi Cadwaladr health board said three hospitals - Wrexham Maelor Hospital, Ysbyty Gwynedd and Ysbyty Glan Clwyd - were facing "significant pressures".
It said extra staff had been called in.
The Ysbyty Gwynedd A&E staff apologised on Saturday and said that they were "struggling".
They urged people to remember to use GP out of hours services and local minor injuries units where possible.
We're so sorry that we are struggling to provide the care our patients deserve today, but are hamstrung by our ED being filled with patients waiting for medical beds, some for past 2 days. Remember, GP Out of Hours & local minor injuries units (e.g. Llandudno) are available too"— Ysbyty Gwynedd ED (@YGEDBangor) December 2, 2017
A health board spokeswoman said the usual winter pressures had been exacerbated by the recent icy spell, which had caused more people to fall.
But she said additional staff had been called in and more beds opened at the three hospitals.
"We're experiencing quite significant pressures at three of our sites which is reflective of the winter pressures and exacerbated by the cold spell," she said,
"We acknowledge staff are challenged and are providing appropriate care to patients and we're extremely grateful and proud of the teams.
"All sites are working extremely hard on patient care and we have put on additional measures, including additional doctors and nurses and we've opened more beds."
The health board had already extended the opening hours for its minor injury units, with them now running until midnight.
A district nurse service - used for people who have not had serious falls - is also being run overnight.