A and E departments are expecting "unprecedented" numbers of people on Monday (29 December).
After an extended Christmas break, the lack of available GP appointments will see more people turning to A and E departments during the holiday period.
Dr Denise Langhor, an A&E consultant at Arrowe Park Hospital on the Wirral, told Sky News: "With Christmas Day and Boxing Day falling on a Thursday and Friday and then the weekend, it's essentially a four-day bank holiday weekend. We are expecting unprecedented levels of attendances on Monday.
"We know last year after Christmas and Boxing Day that our attendances the first normal working day after that increased by a third. It's probably going to be worse this year because the whole of the NHS is currently under immense strain and there's been more attendances this winter since records began," she explained.
"But obviously this time it's a four day bank holiday weekend. We are expecting extreme pressure and a lot of difficulties."
Waiting times in A&E departments hit record levels during the winter, with hospitals failing to meet the target of a maximum four hours waiting time.
It was reported that patients were left waiting on trolleys for extended periods of time before they were seen by doctors, leaving ambulance queues building up outside departments while patients were kept waiting for beds.
Dr Langhor said it is extremely stressful "when people are on the corridor still in the care of the paramedics they could potentially be unwell and needing a space. The other bad things about having paramedics queuing in our corridor is they're not out there on the streets, answering the 999 calls which is where they really need to be."
Anyone with a more minor ailment or injury is advised to seek help at walk-in centres or wait for a GP appointment.
Senior nurse Helen Morris said: "When we have people that turn up that could alternatively go to a walk-in centre, an urgent care centre, a dentist, these are the minor injuries that don't necessarily need to come in but obviously will take the time of both the nurses and doctors away from the patients that really need it."
Extra staff have been brought in to deal with the huge numbers of patients expected on Monday (29 December).