Hospitals across West Yorkshire are urging people to only attend in an emergency after they faced an influx of patients.
Nearly 1,200 people were admitted to hospitals in Wakefield, Pontefract and Dewsbury last week - a record number in one week.
Managers at the Mid Yorkshire Hospitals NHS Trust had to implement their major incident plan for 24 hours, bringing in extra staff.
Between December 20 and 26, 1,194 people were admitted to the three hospitals as an emergency, compared to 1,133 during the same period in 2009.
Tracey McErlain-Burns, acting chief executive at the Mid Yorkshire Hospitals NHS Trust, said staff had responded in an "exemplary way" and added that though many patients were very ill, a large number had minor ailments such as flu-like symptoms which could have been treated elsewhere or at home.
"As always, I would advise anyone with a serious condition or injury to go to the Emergency Department immediately," she added. "However, it is important to stress to local communities that colleagues in primary care, GPs and district nurses are providing alternatives to hospitals for the management of non-urgent and emergency, lifesaving care.
"Please use Emergency Department services appropriately as inappropriate use puts even more pressure on our hospitals and staff."
In Leeds, on some days an additional 100 patients have been going to accident and emergency units at Leeds General Infirmary and St James's Hospital.
Ruth Holt, chief nurse at Leeds Teaching Hospitals said: "This has led to increased waiting times as well as pressure on beds when unexpectedly high numbers of patients need admitting. Our staff are working incredibly hard to cope.
"We would stress that A&E is for emergencies and serious illnesses and would urge our patients to consider all other options."
She added it was particularly important that otherwise healthy patients with colds or flu did not attend hospital as they were likely to infect others.
"We would urge anyone with flu-like symptoms or other illnesses such as diarrhoea and vomiting to avoid visiting relatives or friends who are in hospital. If in any doubt please stay away and keep your germs at home," she said.
Alternatives to going to hospital include visiting NHS Walk-in Centres, Minor Injuries Units, pharmacies and GP-led centres.
For help and advice, contact the 24-hour West Yorkshire Urgent Care Service on 0345 605 9999 or NHS Direct on 0845 4647